The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
"Speak only words of kindness."--This story was told by the Master while at Jetavana, about the bitter words spoken by the Six 1. For, in those days the six, when they disagreed with respectable Brethren, used to taunt, revile and jeer them, and load them with the ten kinds of abuse. This the Brethren reported to the Blessed One, who sent for the Six and asked whether this charge was true. On their admitting its truth, he rebuked them, saying, "Brethren, hard words gall even animals: in bygone days an animal made a man who had used harsh language to him lose a thousand pieces." And, so saying, he told this story of the past.
Once on a time at Takkasilā in the land of Gandhāra there was a king reigning there, and the Bodhisatta came to life as a bull. When he was quite a tiny calf, he was presented by his owners to a brahmin who came in--they being known to give away presents of oxen to such-like holy men. The brahmin called it Nandi-Visāla (Great-Joy), and treated it like his own child, feeding the young creature on rice-gruel and rice. When the Bodhisatta grew up, he thought thus to himself, "I have been brought up by this brahmin with great pains, and all India cannot show the bull which can draw what I can. How if I were to repay the brahmin the cost of my nurture by making proof of my strength?" Accordingly, one day he said to the brahmin, "Go, brahmin, to some merchant rich in herds, and wager him a thousand pieces that your bull can draw a hundred loaded carts."
The brahmin went his way to a merchant and got into a discussion with him as to whose oxen in. the town were the strong. "Oh, so-and-so's, or so-and-so's," said the merchant. "But," added he, "there are no oxen in the town which can compare with mine for real strength." Said the brahmin, "I have a bull who can pull a hundred loaded carts." "Where's such a bull to be found?" laughed the merchant. "I've got him at home," said the brahmin. "Make it a wager." "Certainly," said the brahmin, and staked  a thousand pieces. Then he loaded a hundred carts with sand, gravel, and stones, and leashed the lot together, one behind the other, by cords from the axle-tree of the one in front to the trace-bar of its successor. This done, he bathed Nandi-Visāla, gave him a measure of perfumed rice to eat, hung a garland round his neck, and harnessed him all
alone to the leading cart. The brahmin in person took his seat upon the pole, and flourished his goad in the air, shouting, "Now then, you rascal! pull them along, you rascal!"
"I'm not the rascal he calls me," thought the Bodhisatta to himself; and so he planted his four feet like so many posts, and budged not an inch.
Straightway, the merchant made the brahmin pay over the thousand pieces. His money gone, the brahmin took his bull out of the cart and went home, where he lay down on his bed in an agony of grief. When Nandi-Visāla strolled in and found the brahmin a prey to such grief, he went up to him and enquired if the brahmin were taking a nap. "How should I be taking a nap, when I have had a thousand pieces won of me?" "Brahmin, all the time I have lived in your house, have I ever broken a pot, or squeezed up against anybody, or made messes about?" "Never, my child." "Then, why did you call me a rascal? It's you who are to blame, not I. Go and bet him two thousand this time. Only remember not to miscall me rascal again." When he heard this, the brahmin went off to the merchant, and laid a wager of two thousand. Just as before, he leashed the hundred carts to one another and harnessed Nandi-Visāla, very spruce and fine, to the leading cart. If you ask how he harnessed him, well, he did it in this way:--first, he fastened the cross-yoke on to the pole; then he put the bull in on one side, and made the other fast by fastening a smooth piece of wood from the cross-yoke on to the axletree, so that the yoke was taut and could not skew round either way. Thus a single bull could draw a cart made to be drawn by two. So now seated on the pole, the brahmin stroked Nandi-Visāla on the back, and called on him in this style, "Now then, my fine fellow! pull them along, my fine fellow!" With a single pull the Bodhisatta tugged along the whole string of the hundred carts  till the hindermost stood where the foremost had started. The merchant, rich in herds, paid up the two thousand pieces he had lost to the brahmin. Other folks, too, gave large sums to the Bodhisatta, and the whole passed into the hands of the brahmin. Thus did he gain greatly by reason of the Bodhisatta.
Thus laying down, by way of rebuke to the Six, the rule that hard words please no one, the Master, as Buddha, uttered this stanza:--
When he had thus ended his lesson as to speaking only words of kindness, the Master identified the Birth by saying, "Ānanda was the brahmin of those days, and I myself Nandi-Visāla."
[Note. The substance of this story occurs in the Vinaya, Vol. IV. page 5.]
71:1 The 'Six' were notorious Brethren who are always mentioned as defying the rules of the Order.