Please see Vaikra (Leviticus) 15:31 and Bemidbar (Numbers) 19:13. It is being implied there.

31 Thus shall ye separate the children of Israel from their uncleanness; that they die not in their uncleanness, when they defile My tabernacle that is in the midst of them.

13 Whosoever toucheth the dead, even the body of any man that is dead, and purifieth not himself--he hath defiled the tabernacle of the LORD--that soul shall be cut off from Israel; because the water of sprinkling was not dashed against him, he shall be unclean; his uncleanness is yet upon him.

This tells us that the the body is the temple of Hashem/God.

Rabbis and Sages have been teaching for thousands of years that The first five commandments go together with the five last.1 and 6,2 and 7 and so on? And this explains the commandments:

1 You shall have no other gods before Me.
...
6.You shall not murder.

The rabbis also talk about how the soul travel into the mother and how she is build to receive a soul.

11 Biblical condemnations of abortion…

1. Attempted murder of Jesus Christ whatever you do to the least of these you do to me Matt 25:40

2. Abortion is hatred of God all those who love death hate God Prov 8:36

3. Violates the greatest Commandment. Love God with all your heart, soul, strength and mind Matt 22:37-38, Luke 10:27, Mark12:30

4. Violates the second greatest Commandment. Love our neighbor as yourself, most of all her baby Matt 22:39, Mark 12:31, Galatians 5:14

5. Abortion is UNTHINKABLE to God never entered God’s mind that a mother would sacrifice her baby Jer 7:31, 19:5, 32:35 three times emphasized

6. Abortion is an UNSPEAKABLE evil shameful to even speak of abortion Eph 5:12

7. Defies God’s Commandment “THOU SHALL NOT MURDER”. Premeditated murder of her defenseless, innocent son or daughter - Exodus 20:13, Deut 5:17, Matt 5:21, Matt 19:18, Mark 10:19, Luke 18:20, Romans 13:9, James 2:11, Exodus 23:7, Dan 13:53

8. She has profaned Gods Holy Name Jer 7:31, 19:5, 32:35, Lev 18:21, 20:1-5

9. Abortion is todays child sacrifice to Satan
   Jer 7:31, 19:5, 32:35, Lev 18:21, 20:1-3

10. Abortion is todays Massacre of the Holy Innocents Matt 2:16

11. If she kills her baby then God will kill her Ex 22:22-24

Plus 41 other passages that I don’t have room for

Humans Bear the Image of God

Genesis 9:5-6 (NASB) (emphasis added)

“I certainly will require your lifeblood; from every animal I will require it. And from every person, from every man as his brother I will require the life of a person

“Whoever sheds human blood, By man his blood shall be shed, For in the image of God He made mankind

This command to Noah (and as far as I can tell, to all subsequent generations) seems to be fairly straightforward about murder (i.e. unjustified killing): absolutely prohibited and the appropriate punishment is execution. Anyone made in God's image has this protection by God, and I would argue that an unborn child is as much an image bearer as anyone else.

Is Killing an Unborn Child Murder?

If the question is really something about: Is killing an unborn child murder?, then I don't know if there's a statement in the Bible that will directly answer the question.

The mention of pregnant women found in the Mosaic law (mentioned by others, e.g. Ex 21) may seem to suggest that unborn children are sufficiently human to incur the penalty of execution. Two verses earlier, however, slaves are referred to as property, and injuring one (without killing him) does not have any stated punishment. Killing a slave would result in (unstated) punishment. This isn't entirely explicit regarding the question of humanity.

The simple argument here is that everyone in the Bible talks and acts like an unborn child is human. This is not an explicit statement, but is a meaningful argument from the text. Elizabeth describes the unborn child as "a baby" (Lk 1:41), the word there, βρέφος, being the word used for born and unborn children.

Sacrificing (born) children seems similarly abhorrent to God. Regarding parents burning their children as sacrifices, God says, "nor did it ever enter my mind," (Jer 19:5) seemingly stronger-than-average condemnation for sin.

Bearing the image of God seems to be the mark of humanity that makes murder abhorrent. I see no attempt in the Scriptures to say precisely when this mark of distinction becomes a reality. It seems that the simplest answer that makes sense of what we have, as well as nearly universal experience, is that the moment we know that a woman is pregnant, we start behaving as if it's fully human.

I can think of no way to meaningfully draw a line between two events or milestones after conception where one could argue that the image of God wasn't there, and then was there. Logically, I could only say that after the moment of conception, the image of God must be there.

Are Unfertilized Eggs Human?

This is a trickier question, for which I find even less in the Scriptures. At no point are women commanded to get pregnant rather than menstruate. Menstruation is never characterized as bad in any way, except perhaps for making a woman ceremonially unclean for a week under the Law of Moses—certainly nothing like the penalty for murder. (Lev 15:19-20) It happens without her consent, by God's design, and so I could, perhaps, draw a line between an unfertilized egg and a fertilized one, because a fertilized one begins to show the hallmarks of being fully human. Prior to that, the egg never really grows (once it's mature), and it would be hard to describe it has fully human. "Half human" might be apropos ("haploid" in terms of chromosomes), but is half human enough human?

The fact that a woman's body periodically sheds eggs makes me think that they are not yet alive or human. I cannot find justification in the text for this, but it seems that it is the assumption by the Biblical authors that a menstruating woman is normal, not wicked, and that there's never any description of mourning for the issue from her body. Essentially, it's not alive; not human.

The Church Fathers clearly considered abortion murder. The Didache - a very early Christian writing that pre-dates some of the New Testament Scriptures - stated:

Thou shalt not murder a child by abortion nor kill that which is begotten [2:2]

Barnabas, writing around 80 AD, stated almost the same thing in his Epistle:

Thou shalt not slay the child by procuring abortion; nor, again, shalt thou destroy it after it is born [19:10]

The same prohibition is conveyed in the writings of Athenagoras (c. 175), Tertullian (c. 202), Hippolytus (c. 210), Basil the Great (c. 347), and John Chrysostom (c. 400).

If we accept the beliefs expressed in the early Church that abortion is murder, as the Fathers suggest, then the Mosaic commandment against murder (Exocus 20:13), re-emphasized by Christ (Matthew 19:18, Mark 10:19, Luke 18:20), should serve as an adequate biblical basis for those who seek one, assuming, of course, that one believes that disobeying a commandment of God is, in fact, immoral.

I'd like to make a few secular/political contributions to this question. This answer probably should not qualify for the accepted answer, but I think it's worth adding here that there are some good scientific legal arguments against abortion, and it's not solely an issue of religion vs science.

Abortion iswas legal in the United States because of the 1973 Roe v Wade decision. The ruling in this case specifically declined to look at whether or not a fetus is a human life. The justices attempted to side-step that polarizing issue. They could not settle the question, and so dealt with the fetus as merely a "potential" human life. I believe they hoped this would assuage the religious side by still treating the unborn as something special, as well as the secular side by declining to rule that a fetus was fully human. Regardless of their intent, the court took that baseline and then weighed whether the mother's right to privacy can exceed a mere potential human's right to life and the interest of the state in protecting that potential life — thus giving in by default to the secular view — and finds, to a point, in favor of the mother. That point, which was originally very limited, has today been stretched to breaking.

If the court's view of a fetus is sound, then the current prevailing secular position on abortion absolutely makes sense. A women should, moral issues aside and purely from a legal standpoint, be able to do with her own body as she pleases. However, if this is wrong — if a fetus is its own separate human life form, and more than just human in potentia — then the opposite view absolutely makes sense, and most (not all!) abortions are nothing short of state-sanctioned murder. It's also worth noting that, ethics aside and based solely on the science of the time, the court's view of a fetus was not entirely without merit.

However, science has learned some things since 1973. I'm talking here, of course, about DNA. While DNA has been known since the 1800's, it wasn't until the 1950's that scientists really began to understand it.¹ The forensic and legal worlds took a little longer to embrace this, and it wasn't until 1986 that DNA is first used in court to exonerate and 1987 for conviction² — well after Roe v Wade.

Today, I think most would agree that no other physical property more than DNA absolutely and definitively distinguishes one individual from another. DNA is used in courts to distinguish and prove not only individuals, but also family relationships and, most significantly here, different species. If the situation were examined again today, a DNA sample from a fetus would undoubtedly show that fetal tissue is both distinct from the mother and also entirely human. While I have not, of course, had the opportunity to confirm this, it is my (admittedly limited) understanding of animal biology that a hypothetical DNA sample taken from a fetus would be a match for that of the adult, should the fetus continue to develop and ultimately reach that stage of life.

The significance here is that fetal tissue, having distinct human DNA, should probably no longer be considered as merely a part of the mother's body. Take religion out of the debate completely, and the science says that a fetus is both fully human and separate from the mother. A woman has the right to do with her own body what she wants... but now we have the rights of another individual involved as well. A woman has the right to do with her own body what she wants... but the scientific evidence shows that the fetus is more than just part of the mother's body.

Now we must take this new understanding of the scientific evidence into account, and use it to re-examine the current legal environment. Since an unborn fetus is a definitely a distinct human entity, as demonstrated by it's DNA, and more than a mere potential human as it was treated by Roe v Wade, we can say the current Supreme Court ruling is clearly inadequate. A new ruling must be established, and this can only be (re-)settled by the courts. But my opinion is that a much better legal interpretation of this new evidence would make use of same legal doctrine that allows the use of a murder victim's corpse for forensic purposes, even over the objections of next of kin. In this context, we can say that the unborn individual would likely want to live, and that the state has the power to compel the mother to allow this. Doubtless those in favor of legal abortions will come up with their own arguments, but as they have as yet largely declined to move beyond Roe v Wade, I haven't heard anything more compelling.

As a complete aside to the question, it boggles my mind that Pro-Life groups continue today to make religious arguments for their position against people who will only acknowledge arguments grounded in a framework of science, when there is a perfectly good scientific argument for the Pro-Life position ready and waiting. I agree with the religious argument as well, but as Levar Burton said, "You don't have to take my word for it.", when there is (to the Pro-Choice view) a more credible source at hand. I feel like pushing the DNA argument more strongly could change the conversation about the issue and tilt more opinions in the Pro-Life direction. I've heard it said by some on the Pro-Choice side that those who are Pro-Life hate women. Surely they understand that this argument reciprocates and, if true, by their own logic and arguments Pro-Choice groups hate children.

^[1] History of DNA research (Wikipedia)
^[2] DNA profiling (Wikipedia)

A wide variety of scripture can be cited in obvious support of abortion (as an act of murder) is inherently immoral:

Jeremiah 1:5

Before I formed you in the womb I knew you, And before you were born I consecrated you; I have appointed you a prophet to the nations.

Psalm 139:5

For You formed my inward parts; You wove me in my mother’s womb.

Exodus 20:13

You shall not murder.

Ephesians 1:4

just as He chose us in Him before the foundation of the world, that we would be holy and blameless before Him

If God wove us in our mother's womb and knew us before the foundation of the world, and murder is a sin (ie is "immoral"), then abortion is murder and is immoral.