The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
"Untiring, deep they dug."--This discourse was delivered by the Blessed One whilst he was dwelling at Sāvatthi.
About whom, you ask?
About a Brother who gave up persevering.
Tradition says that, whilst the Buddha was dwelling at Sāvatthi, there came to Jetavana a scion of a Sāvatthi family, who, on hearing a discourse by the Master, realised that Lusts breed suffering, and was admitted to the first stage of the Brotherhood. After five years passed in preparing for admission to full Brotherhood 1, when he had learnt two summaries and had trained himself in the methods of Insight, he obtained from the Master a theme for meditation which commended itself to him. Retiring to a forest, he passed there the rainy season; but for all his striving during the three months, he could not develope a glimmer or an inkling of Insight. So the thought came to him, "The Master said there were four types of men, and I must belong to the lowest of all; in this birth, methinks, there is neither Path nor Fruit for me. What good shall I do by living in the forest? Back to the Master I will go, and live my life beholding the glories of the Buddha's presence and listening to his sweet teachings." And back again to Jetavana he came.
Now his friends and intimates said, "Sir, it was you who obtained from the Master a theme for meditation and departed to live the solitary life of a sage. Yet here you are back again, going about enjoying fellowship. Can it be that you have won the crown of the Brothers vocation and that you will never know re-birth?" "Sirs, as I won neither Path nor Fruit, I felt myself doomed to futility, and so gave up persevering and came back." "You have done wrong, Sir, in shewing a faint heart when you had devoted yourself to the doctrine of the dauntless Master.  Come, let us bring you to the Buddha's notice." And they took him with them to the Master.
When the Master became aware of their coming, he said, "Brethren, you bring with you this Brother against his will. What has he done?"
"Sir, after devoting himself to so absolutely true a doctrine, this Brother has given up persevering in the solitary life of a sage, and is come back."
Then said the Master to him, "Is it true, as they say, that you, Brother, have given up persevering?" "It is true, Blessed One." "But how comes it that, after devoting yourself to such a doctrine, you, Brother, should be the one to show yourself not a man desiring little, contented, solitary, and determined, but a man lacking perseverance? Was it not you who were so stout-hearted in bygone days? Was it not by you single-handed, thanks to your perseverance, that in a sandy desert the men and the oxen belonging to a caravan of five hundred carts got water and were cheered? And how is it that, now, you are giving in?" These words sufficed to give heart to that Brother.
Hearing this talk, the Brethren asked the Blessed One, saying, "Sir, the present faintheartedness of this Brother is clear to us; but hidden from us is the knowledge of how, by the perseverance of this single man, the men and oxen got water in a sandy desert and were cheered. This is known only to you who are omniscient; pray tell us about it."
"Hearken, then, Brethren," said the Blessed One; and, having excited their attention, he made clear the thing that re-birth had concealed from them.
Once on a time when Brahmadatta was king in Benares in Kāsi the Bodhisatta was born into a trader's family. When he was grown up, he used to travel about trading with 500 carts. On one occasion he came to a sandy wilderness sixty leagues across, the sand of which was so fine that, when grasped, it slipped through the fingers of the closed fist. As soon as the sun got up, it grew as hot as a bed of charcoal-embers and nobody could walk upon it. Accordingly, those traversing it used to take fire-wood, water, oil, rice and so forth on their carts, and only travelled by night. At dawn they used to range their carts in a circle to form a laager, with an awning spread overhead, and after an early meal used to sit in the shade all the day long. When the sun went down, they had their evening meal; and, so soon as the ground became cool, they used to yoke their carts and move forward. Travelling on this desert was like voyaging over the sea; a 'desert-pilot,' as he was called, had to convoy them over by knowledge of the stars . And this was the way in which our merchant was now travelling that wilderness.
When he had only some seven more miles before him, he thought to himself, "To-night will see us out of this sandy wilderness." So, after they had had their supper, he ordered the wood and water to be thrown away, and yoking his carts, set out on the road. In the front cart sat the pilot upon a couch looking up to the stars in the heavens and directing the course thereby. But so long had he been without sleep that he was tired out and fell asleep, with the result that he did not mark that the oxen had turned round and were retracing their steps. All night the oxen kept on their way, but at dawn the pilot woke up, and, observing the disposition of the stars overhead, shouted out, "Turn the carts round!
turn the carts round!" And as they turned the carts round and were forming them into line, the day broke. "Why this is where we camped yesterday," cried the people of the caravan. "All our wood and water is gone, and we are lost." So saying, they unyoked their carts and made a laager and spread the awning overhead; then each man flung himself down in despair beneath his own cart. Thought the Bodhisatta to himself, "If I give in, every single one will perish." So he ranged to and fro while it was still early and cool, until he came on a clump of kusa-grass. "This grass," thought he, "can only have grown up here thanks to the presence of water underneath." So he ordered a spade to be brought and a hole to be dug at that spot. Sixty cubits down they dug, till at that depth the spade struck on a rock, and everybody lost heart. But the Bodhisatta, feeling sure there must be water under that rock, descended into the hole and took his stand upon the rock. Stooping down, he applied his ear to it, and listened. Catching the sound of water flowing beneath, he came out and said to a serving-lad, "My boy, if you give in, we shall all perish. So take heart and courage. Go down into the hole with this iron sledge-hammer, and strike the rock."
Obedient to his master's bidding,  the lad, resolute where all others had lost heart, went down and struck the rock. The rock which had dammed the stream, split asunder and fell in. Up rose the water in the hole till it was as high as a palm-tree; and everybody drank and bathed. Then they chopped up their spare axles and yokes and other surplus gear, cooked their rice and ate it, and fed their oxen. And as soon as the sun set, they hoisted a flag by the side of the well and travelled on to their destination. There they bartered away their goods for twice and four times their value. With the proceeds they returned to their own home, where they lived out their term of life and in the end passed away to fare thereafter according to their deserts. The Bodhisatta too after a life spent in charity and other good works, passed away likewise to fare according to his deserts.
When the Supreme Buddha had delivered this discourse, he, the All-Knowing One himself, uttered this stanza:
 This discourse ended, he preached the Four Truths, at the close whereof the fainthearted Brother was established in the highest Fruit of all, which is Arahatship.
Having told these two stories, the Master established the connexion linking them both together, and identified the Birth by saying:--"This fainthearted Brother of to-day was in those days the serving-lad who, persevering, broke the rock and gave water to all the people; the Buddha's followers were the rest of the people of the caravan; and I myself was their leader."
9:1 The terms pabbajjā and upasampadā, which denote the two stages of initiation for a Brother of the Buddhist Order, and are comparable with the successive degrees of Bachelor and Master in a Faculty, suggest the successive ordinations of Deacon and Priest. But, as it is misleading to use Christian phraseology in speaking of the Buddhist philosophy, these convenient terms have been eschewed in the translation. As will be seen from the Vinaya (Mahāvagga I. 49-51), fifteen was the normal age for pabbajjā and twenty for upasampadā, the interval being that of five years mentioned in the text.