The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
"When gladness."--This story was told by the Master while at Sāvatthi, about a certain Brother. Tradition says that through hearing the Master preach a young gentleman of Sāvatthi gave his heart to the precious Faith 1 and became a Brother. His teachers and masters proceeded to instruct him in the whole of the Ten Precepts of Morality, one after the other, expounded to him the Short, the Medium, and the Long Moralities 2, set forth the Morality which rests on self-restraint according to the Pātimokkha 3, the Morality which rests on self-restraint as to the Senses, the Morality which rests on a blameless walk of life, the Morality which relates to the way a Brother may use the Requisites. Thought the young beginner, "There is a tremendous lot of this Morality; and I shall undoubtedly fail to fulfil all I have vowed. Yet what is the good of being a brother at all, if one cannot keep the rules of Morality? My best course is to go back to the world, take a wife and rear children, living a life of almsgiving and other good works." So he told his superiors what he thought, saying that he proposed to return to the lower state of a layman, and wished to hand back his bowl and robes. "Well, if it be so with you," said they, "at least take leave of the Buddha before you go;" and they brought the young man before the Master in the Hall of Truth.
"Why, Brethren," said the Master, "are you bringing this Brother to me against his will?"
"Sir, he said that Morality was more than he could observe, and wanted to give back his robes and bowl. So we took him and brought him to you."
"But why, Brethren," asked the Master, "did you burthen him with so much? He can do what he can, but no more. Do not make this mistake again, and leave me to decide what should be done in the case."
Then, turning to the young Brother, the Master said, "Come, Brother; what concern have you with Morality in the mass? Do you think you could obey just three moral rules?"
"Oh, yes, Sir."
"Well now, watch and guard the three avenues of the voice, the mind, and the body; do no evil whether in word, or thought, or act. Cease not to be a Brother, but go hence and obey just these three rules."
"Yes, indeed, Sir, I will keep them," here exclaimed the glad young man, and back he went with his teachers again. And as he was keeping his three rules, he thought within himself, "I had the whole of Morality told me by my instructors; but because they were not the Buddha, they could not make me grasp even this much. Whereas  the All-Enlightened One, by reason of his Buddhahood, and of his being the Lord of Truth, has expressed so much Morality in only three rules concerning the Avenues, and has made me understand it clearly. Verily, a very present help has the Master been to me." And
he won Insight and in a few days attained Arahatship. When this came to the ears of the Brethren, they spoke of it when met together in the Hall of Truth, telling how the Brother, who was going back to the world because he could not ho to fulfil Morality, had been furnished by the Master with three rules embodying the whole of Morality, and had been made to grasp those three rules, and so had been enabled by the Master to win Arahatship. How marvellous, they cried, was the Buddha.
Entering the Hall at this point, and learning on enquiry the subject of their talk, the Master said, "Brethren, even a heavy burthen becomes light, if taken piecemeal; and thus the wise and good of past times, on finding a huge mass of gold too heavy to lift, first broke it up and then were enabled to bear their treasure away piece by piece." So saying, he told this story of the past.
Once on a time when Brahmadatta was reigning in Benares, the Bodhisatta came to life as a farmer in a village, and was ploughing one day in a field where once stood a village. Now, in bygone days, a wealthy merchant had died leaving buried in this field a huge bar of gold, as thick round as a man's thigh, and four whole cubits in length. And full on this bar struck the Bodhisatta's plough, and there stuck fast. Taking it to be a spreading root of a tree, he dug it, out; but discovering its real nature, he set to work to clean the dirt off the gold. The day's work done, at sunset he laid aside his plough and gear, and essayed to shoulder his treasure-trove and walk off with it. But, as he could not so much as lift it, he sat down before it and fell a-thinking what uses he would put it to. "I'll have so much to live on, so much to bury as a treasure, so much to trade with, and so much for charity and good works," thought he to himself, and accordingly cut the gold into four. Division made his burthen easy to carry; and he bore home the lumps of gold. After a life of charity and other good works, he passed away to fare thereafter according to his deserts.
His lesson ended, the Master, as Buddha, recited this stanza:-- 
And when the Master had thus led his teaching up to Arahatship as its crowning point, he shewed the connexion and identified the Birth by saying, "In those days I myself was the man who got the nugget of gold."
140:1 Or perhaps ratanasāsanaṁ means 'the creed connected with the (Three) Gems,' viz. the Buddha, the Doctrine, and the Order.
140:2 These are translated in Rhys Davids' "Buddhist Suttas," pp. 189-200.
140:3 The Pātimokkha is translated and discussed in Pt. I. of the translation of the Vinaya by Rhys Davids and Oldenberg (S. B. E. Vol. 13).