The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
"May shame."--This story was told by the Master while at Jetavana about Sāriputta, the Captain of the Faith. Tradition says that in the days when the Elder used to eat meal-cakes, folks came to the monastery with a quantity of such cakes for the Brotherhood. After the Brethren had all eaten their fill, much remained over; and the givers said, "Sirs, take some for those too who are away in the village."
Just then a youth who was the Elder's co-resident, was away in the village. For him a portion was taken; but, as he did not return, and it was felt that it was getting very late 1, this portion was given to the Elder. When this portion had been eaten by the Elder, the youth carte in. Accordingly, the Elder explained the case to him, saying, "Sir, I have eaten the cakes set apart for you." "Ah!" was the rejoinder, "we have all of us got a sweet tooth." The Great Elder was much troubled.
"From this day forward," he exclaimed, "I vow never to eat meal-cakes again." And from that day forward, so tradition says, the Elder Sāriputta never touched meal-cakes again! This abstention became matter of common knowledge in the Brotherhood, and the Brethren sat talking of it in the Hall of Truth. Said the Master, "What are you talking of, Brethren, as you sit here?" When they had told him, he said, "Brethren, when Sāriputta has once given anything up, he never goes back to it again, even though his life ḅe at stake." And so saying, he told this story of the past.
Once on a time, when Brahmadatta was reigning in Benares, the Bodhisatta was born into a family of doctors skilled in the cure of snake-bites, and when he grew up, he practised for a livelihood.
Now it fell out that a countryman was bitten by a snake; and without delay his relatives quickly fetched the doctor. Said the Bodhisatta, "Shall I extract the venom with the usual antidotes, or have the snake caught and make it suck its own poison out of the wound?" "Have the snake caught and make it suck the poison out." So, he had the snake caught, and asked the creature, saying "Did you bite this man?" "Yes, I did," was the answer.  "Well then, suck your own poison out of the wound again." "What? Take back the poison I have once shed!" cried the snake; "I never did, and I never will." Then the doctor made a fire with wood, and said to the snake, "Either you suck the poison out, or into the fire you go."
"Even though the flames be my doom, I will not take back the poison I have once shed," said the snake, and repeated the following stanza:--
With these words, the snake moved towards the fire! But the doctor barred its way, and drew out the poison with simples and charms, so that the man was whole again. Then he unfolded the Commandments to the snake, and set it free, saying, "Henceforth do harm to none."
And the Master went on to say,--"Brethren, when Sāriputta has once parted with anything, he never takes it back again, even though his life be at stake." His lesson ended, he shewed the connexion and identified the Birth by saying, "Sāriputta was the snake of those days, and I the doctor."
167:1 i.e. close on to mid-day, after which the food could not properly be eaten. See note, page 107.