Was the Buddha a bodhisattva (for the benefit of all) before his awakening?

The Jataka Tales (which is in the fifth Nikaya) say "Bodhisattva".

See also Buddha's past lives in the Pali Suttas outside of Jataka and Where is the description of the vow and the Bodhi tree?

"Bodhisattva" is a reification, just like "a Buddha". To say that "Bodhisattva is a reification" - is, too, a reification. "For the benefit of all" is a reification. "For" and "benefit" and "all" - are reifications as well.

Śāriputra: How then should the Bodhisattva, the great being, course in perfect wisdom?

The Lord: Here the Bodhisattva, the great being, coursing in the perfection of wisdom, truly a Bodhisattva, does not review a Bodhisattva, nor the word "Bodhisattva", nor the course of a Bodhisattva, (nor the perfection of wisdom, nor the word "perfection of wisdom". He does not review that "he courses", nor that "he does not course"). He does not review form, feeling, perception, formative forces, or consciousness. And why? Because the Bodhisattva, the great being, is actually empty of the own-being of a Bodhisattva, and because perfect wisdom is by its own-being empty. And why? That is its essential original nature. (For it is not through emptiness that form etc. is empty.) Nor is emptiness other than form, etc.

And why? The very form, etc., is emptiness, the very emptiness is form, etc. And why? Because "Bodhisattva", "perfect wisdom", "form", etc. are mere words. Because form, etc., are like an illusion. Illusions and mere words do not stand at any point or spot; they are not, do not come into being, are false to behold. For of what the own-being is seen to be an illusion, of that there is no production or stopping, no defilement or purification. Thus a Bodhisattva, a great being who courses in the perfection of wisdom, also does not review the production (of any dharma); nor its stopping (or abiding, its decrease or increase), defilement or purification. (He does not review form, etc., nor "enlightenment", nor what is called an "enlightenment-being".) And why? Because words are artificial. People have constructed a counter-dharma. They express it conventionally by means of an adventitious designation (which is imagined and unreal, and they settle down in that conventional expression). A Bodhisattva, a great being who courses in perfect wisdom, does not review (that which is said to correspond to) all those words, (does not get at them). Not reviewing them, (not getting at them, he does not mind them), does not settle down in them.

Furthermore, a Bodhisattva, a great being who courses in the perfection of wisdom, does not consider the fact that these are mere words, i.e. this "Bodhisattva", this "enlightenment", this "Buddha", this "perfection of wisdom", this "coursing in the perfection of wisdom", this "form", etc. Just as one speaks of a "self, and yet no self is got at, and no being, soul, personality, person, individual, or man, etc., on account of unascertainable emptiness. And why? Because there a Bodhisattva does also not review that by means of which he would settle down. Coursing thus, a Bodhisattva, a great being courses in perfect wisdom.

(from The Large Sutra on Perfect Wisdom, translated by E.Conze)

Additional detail on the bodhisattva Gautama’s reflection that motivated him to set out on his quest can be gathered from another occurrence of the ‘before awakening’ phrase, found in the Discourse on the Noble Quest, the Ariyapariyesanā-sutta, and in its Madhyama-āgama parallel. The two discourses contrast an average person’s quest for worldly things that are subject to decay and death to the noble quest for what is not subject to decay and death. Both reveal that this noble quest motivated the bodhisattva to go forth in search of awakening, presenting his reflection in nearly identical terms:

“Being myself subject to old age … and death, now suppose I were to search for what is free from old age … and death, for the unsurpassable peace from bondage, Nirvāṇa.”
“Being myself truly subject to old age and death … suppose I were to search … for what is free from old age and death … for the unsurpassable peace from bondage, Nirvāṇa.”

This appears to be the only passage in the Pāli Nikāyas that explicitly formulates what motivated the bodhisattva Gautama to set out in search of awakening. Notably, this formulation does not in any way reflect a concern for others. Rather, according to this autobiographical report the bodhisattva Gautama’s motivation was to find a solution for the problem of being “himself”, attanā/自, subject to old age and death etc.

The same trait recurs in the description of the successful completion of the bodhisattva’s quest, given in the Ariyapariyesanā-sutta and its parallel. According to both versions, having arrived at the unsurpassable peace from bondage that is free from old age and death, Gautama realized that he had fully liberated himself from the prospect of future birth and existence. Here, too, there is no reference at all to being able to save others. Instead, the way the Buddha perceived his own awakening – according to early Buddhist discourse – is formulated entirely in terms of having freed himself.

The conspicuous lack of any concern for others becomes even more prominent with the next episode recorded in the Ariyapariyesanā-sutta, according to which the newly awakened Buddha was disinclined to teach others and decided to rather remain content with having reached liberation himself.

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Such reluctance on the part of the newly awakened Buddha is not easily reconciled with the notion common to all Buddhist traditions that he had prepared himself over immense periods of time with the sole intention of executing the task of leading others to liberation. Judging from the account given in the Ariyapariyesanā-sutta, the reason for the Buddha’s disinclination to teach was that it would be fatiguing (klamatha) and vexing (viheṭhā) for him if others should fail to understand the profound truth he had realized. Similar reasons recur in other reports of his initial hesitation to teach, found in an Ekottarika-āgama discourse, in the Catuṣpariṣat-sūtra, and in the Vinayas of the Dharmaguptaka, Lokottaravāda-Mahāsāṃghika, Mahīśāsaka and (Mūla-)Sarvāstivāda traditions.

That is, when reflecting on the possibility of sharing his discovery with others, according to a range of sources the Buddha considered the matter entirely from the perspective of how it would affect himself. This ties in with the observations made above regarding his motivation and his reaching of the final goal. Throughout, according to these texts the Buddha’s predominant concern is with himself, when he forms his initial motivation to set out for awakening, when he successfully completes his quest, and even when he reflects about what course of action is to be taken next.

This certainly does not imply that from the perspective of the early discourses the Buddha was not compassionate. [...] However, the early discourses do not give any indication that a concern for others was part of the motivation of the bodhisattva Gautama to set out on his quest for awakening, nor does the successful reaching of this goal show any immediate relationship to teaching activity.

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In sum, in early Buddhist thought the compassionate impulse to become active for the sake of others was associated with the Buddha as well as with arhats and those who aspire to become arhats, but was not seen as a quality that motivated the bodhisattva’s quest for awakening.

(from The Genesis of the Bodhisattva Ideal, by Analayo Bhikkhu)