Where did the Buddha speak of his difficulty in eating almsfood as a Bodhisatta?

It is from the The Great Chronicles of the Buddhas by venerable Mingun Sayadaw.

Chapter 4, page 280, paragraph 3. It is preceded by the following.

The Bodhishtta's Visit to Rajagaha City

After becoming a recluse, the Bodhisatta, after spending seven full days in ascetic bliss in the nearby mango grove called Anupiya, travelled a journey of thirty yojanas on foot in one single day and entered the city of Rajagaha. (This is the statement made in the Buddhavamsa Commentary and the Jataka Commentary.) (According to the Sutta Nipata Commentary, however,) the Bodhisatta, after becoming a recluse, observed the Ajivattamaka sila, the Precepts with pure livelihood as the eighth, and journeyed to Rajagaha, thirty yojanas away from the banks of Anoma in seven days.

The quote appears in this text. However it appears to be a Victorian-era translation of the Jâtaka without much details about the version of the original from which it was translated.

BUDDHISM

IN TRANSLATIONS

Passages Selected from the Buddhist Sacred Books

and Translated from the Original Pâli into English by

Henry Clarke Warren

Published by Harvard University Press {1896}

http://www.sacred-texts.com/bud/bits/bits007.htm

§ 7. THE GREAT STRUGGLE. Translated from the Introduction to the Jâtaka (i.6529).

NOW the Future Buddha, having thus retired from the world,--in that place there was a mango-grove named Anupiya, and here he first spent a week in the joy of having retired from the world,--in one day went on foot to Râjagaha, a distance of thirty leagues, and entering the city, he begged for food from house to house without passing any by. By the beauty of the Future Buddha, the whole city was thrown into a commotion, like that into which Râjagaha was thrown by the entrance of Dhanapâlaka, or like that into which the

p. 68 [J.i.664 heavenly city was thrown by the entrance of the chief of the Titans.

Then ran the king's men to the palace, and made announcement,--

"Sire, there is a being of such and such appearance going about the city begging for food. Whether he be a god, or a man, or a serpent, or a bird, we do not know."

Then the king, standing on the roof of his palace, and thence beholding the Great Being, became amazed and astonished, and commanded his men,--

"Look ye now! Go and investigate this! If this person be not a man, he will vanish from sight as soon as he leaves the city; if, namely, he be a god, he will depart by way of the air; if a serpent, he will sink into the ground. But if he be a human being, he will eat the food he has obtained in alms."

Now the Great Being, after collecting a number of scraps, sufficient, as he judged, for his sustenance, left the city by the same gate he had entered, and sitting down with his face to the east, in the shade of Pandava rock, he attempted to eat his meal. But his stomach turned, and he felt as if his inwards were on the point of coming out by his mouth. Thereupon, in the midst of his distress at that repulsive food, --for in that existence he had never before so much as seen such fare,--he began to admonish himself, saying, "Siddhattha, although you were born into a family having plenty to eat and drink, into a station in life where you lived on fragrant third season's rice1 with various sauces of the finest flavors, yet when you saw a monk clad in garments taken from the rubbish heap, you exclaimed, 'Oh, when shall I be like him, and eat food which I have begged? Will that time ever come?' And then you retired from the world. And

p. 69 [J.i.6622 now that you have your wish, and have renounced all, what, pray, is this you are doing?" When he had thus admonished himself, his disgust subsided, and he ate his meal.

I found it in the introduction to the Jatakas, which seems to be the original source:

Now the Great Being, after collecting a number of scraps, sufficient, as he judged, for his sustenance, left the city by the same gate he had entered, and sitting down with his face to the east, in the shade of Pandava rock, he attempted to eat his meal. But his stomach turned, and he felt as if his inwards were on the point of coming out by his mouth. Thereupon, in the midst of his distress at that repulsive food, --for in that existence he had never before so much as seen such fare,--he began to admonish himself, saying, "Siddhattha, although you were born into a family having plenty to eat and drink, into a station in life where you lived on fragrant third season's rice1 with various sauces of the finest flavors, yet when you saw a monk clad in garments taken from the rubbish heap, you exclaimed, 'Oh, when shall I be like him, and eat food which I have begged? Will that time ever come?' And then you retired from the world. And now that you have your wish, and have renounced all, what, pray, is this you are doing?" When he had thus admonished himself, his disgust subsided, and he ate his meal.

-- Jāt-A nidānakathā (from Buddhism In Translations, Henry Clarke Warren, trans.)

The relevant Pali is "antāni parivattitvā mukhena nikkhamanākārappattāni viya ahesuṃ" - It was like the intestines, having churned, attained the state of leaving through the mouth."

The Buddhavamsa doesn't mention this reflection, saying of his first alms round simply:

nisīditvā āhāraṃ paccavekkhitvā nibbikāro paribhuñji

Having sat down, having reflected on the food, unperturbed, he ate.

-- Bv-A, nidānakathā