The Jataka, Vol. II, tr. by W.H.D. Rouse, , at sacred-texts.com
 "What a trifle," etc.--This story the Master told while sojourning in Jetavana, about the twenty-one unlawful ways of earning a livelihood.
At one time there were a great many Brethren who used to get a living by being physicians, or runners, doing errands on foot, exchanging alms for alms 1, and the like, the twenty-one unlawful callings. All this will be set forth in the Sāketa Birth 2. When the Master found out that they got their living thus, the said, "Now there are a great many Brethren who get their living in unlawful ways. Those who get their living thus will not escape birth as goblins or disembodied spirits; they will become beasts of burden; they will be born in hell; for their benefit and blessing it is necessary to hold a discourse which bears its own moral clear and plain." So he summoned the Community together, and said, "Brethren, you must not win your necessaries by the one-and-twenty unlawful methods. Food won unlawfully is like a piece of redhot iron, like a deadly poison. These unlawful methods are blamed and rebuked by disciples of all Buddhas and Pacceka-Buddhas. For those who eat food gained by unlawful means there is no laughter and no joy. Food got in this way, in my religion, is like the leavings of one of the lowest caste. To partake of it, for a disciple of the Religion of the Good, is like partaking of the leavings of the vilest of mankind." And with these words, he told all old-world story.
Once upon a time, when Brahmadatta was king of Benares, the Bodhisatta was born as the son of a man of the lowest caste. When he grew up, he took the road for some purpose, taking for his provision some rice grains in a basket.
At that time there was a young fellow in Benares, named Satadhamma. He was the son of a magnifico, a Northern brahmin. He also took the road for some purpose, but neither rice grains nor basket had he. The two met upon the highway. Said the young brahmin to the other, "What caste are you of?" He replied, "Of the lowest. And what are you?"  "Oh, I am a Northern brahmin." "All right, let us journey together;" and so together they fared along. Breakfast time came: The Bodhisatta sat down where there was some nice water, and washed his hands, and opened his basket. "Will you have some?" said he. "Tut, tut," says the other, "I want none, you low fellow." "All right,"
says the Bodhisatta. Careful to waste none, he put as much as he wanted in a leaf apart from the rest, fastened up his basket, and ate. Then he took a drink of water, washed his hands and feet, and picked up the rest of his rice and food. "Come along, young Sir," says he, and they started off again on their journey.
All day they tramped along; and at evening they both had a bath in some nice water. When they came out, the Bodhisatta sat down in a nice place, undid his parcel, and began to eat. This time he did not offer the other a share. The young gentleman was tired with walking all day, and hungry to the bottom of his soul; there he stood, looking on, and thinking, "If he offers me any, I'll take it." But the other ate away without a word. "This low fellow," thought the young man, "eats every scrap without a word. Well, I'll beg a piece; I can throw away the outside, which is defiled, and eat the rest." And so he did; he ate what was left. As soon as he had eaten, he thought--"How I have disgraced my birth, my clan, my family! Why, I have eaten the leavings of a low born churl!" Keen indeed was his remorse; he threw up the food, and blood came with it. "Oh, what a wicked deed I have done," he wept, "all for the sake of a trifle!" and he went on in the words of the first stanza: 
Thus did the young gentleman make his lamentation; adding, "Why did I do such a wicked thing just for life's sake?" He plunged into the jungle, and never let any eye see him again, but there he died forlorn.
When this story was ended, the Master repeated, "Just as the young brahmin, Brethren, after eating the leavings of a low-caste man, found that neither laughter nor joy was for him, because he had taken improper food; so whosoever has embraced this salvation, and gains a livelihood by unlawful means, when he eats the food and supports his life in any way that is blamed and disapproved by the Buddha, will find that there is no laughter and no joy for him." Then, becoming perfectly enlightened, he repeated the second stanza:
 When this discourse was concluded, the Master declared the Truths and identified the Birth:--at the conclusion of the Truths many Brethren entered upon the Paths and the Fruit thereof:--saying, "At the time of the story I was the low-caste man."
57:1 The offence meant is giving a share of alms on one day, and receiving the like the next day, to save the trouble of seeking alms daily.
57:2 No. 237, which however only refers to no. 68.