The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
 "The man who guards not."--This story was told by the Master while in the Anūpiya Mango-grove near the town of Anūpiya, about the Elder Bhaddiya (the Happy), who joined the Brotherhood in the company of the six young nobles with whom was Upāli 1. Of these the Elders Bhaddiya, Kimbila, Bhagu, and Upāli attained to Arahatship; the Elder Ānanda entered the First Path; the Elder Anuruddha gained all-seeing vision; and Devadatta obtained the power of ecstatic self-abstraction. The story of the six young nobles, up to the events at Anūpiya, will be related in the Khaṇḍahāla-jātaka 2.
The venerable Bhaddiya, who used in the days of his royalty to guard himself as though he were appointed his own tutelary deity, bethought him of the state of fear in which he then lived when he was being guarded by numerous guards and when he used to toss about even on his royal couch in his private apartments high up in the palace; and with this he compared the absence of fear in which, now that he was an Arahat, he roamed hither and thither in forests and desert places. And at the thought he burst into this heartfelt utterance--"Oh, happiness! Oh, happiness!"
This the Brethren reported to the Blessed One, saying, "The venerable Bhaddiya is declaring the bliss he has won."
"Brethren," said the Blessed One, "this is not the first time that Bhaddiya's life has been happy; his life was no less happy in bygone days."
The Brethren asked the Blessed One to explain this. The Blessed One made clear what had been concealed from them by re-birth.
Once on a time when Brahmadatta was reigning in Benares, the Bodhisatta was born a wealthy northern brahmin. Realising the evil of lusts and the blessings that flow from renouncing the world, he abjured lusts, and retiring to the Himalayas there became a hermit and won the eight Endowments. His following waxed great, amounting to five hundred ascetics. Once when the rains set in, he quitted the Himalayas and travelling along on an alms-pilgrimage with his attendant ascetics through village and town came at last to Benares, where he took up his abode in the royal pleasaunce as the pensioner of the king's bounty. After dwelling here for the four rainy months, he came to the king to take his leave. But the king said to him, "You are old, reverend sir. Wherefore should you go back to the Himalayas'? Send your pupils back thither  and stop here yourself."
The Bodhisatta entrusted his five hundred ascetics to the care of his oldest disciple, saying, "Go you with these to the Himalayas; I will stop on here."
Now that oldest disciple had once been a king, but had given up a mighty kingdom to become a Brother; by the due performance of the rites appertaining to concentrated thought he had mastered the eight Endowments. As he dwelt with the ascetics in the Himalayas, one day a longing came upon him to see the master, and he said to his fellows, "Live on contentedly here; I will come back as soon as I have paid my respects to the master." So away he went to the master, paid his respects to him, and greeted him lovingly. Then he lay down by the side of his master on a mat which he spread there.
At this point appeared the king, who had come to the pleasaunce to see the ascetic; and with a salutation he took his seat on one side. But though he was aware of the king's presence, that oldest disciple forbore to rise, but still lay there, crying with passionate earnestness, "Oh, happiness! Oh, happiness!"
Displeased that the ascetic, though he had seen him, had not risen, the king said to the Bodhisatta, "Reverend sir, this ascetic must have had his fill to eat, seeing that he continues to lie there so happily, exclaiming with such earnestness."
"Sire," said the Bodhisatta, "of old this ascetic was a king as you are. He is thinking how in the old days when he was a layman and
lived in regal pomp with many a man-at-arms to guard him, he never knew such happiness as now is his. It is the happiness of the Brother's life, and the happiness that Insight brings, which move him to this heartfelt utterance." And the Bodhisatta further repeated this stanza to teach the king the Truth:--
[paragraph continues]  Appeased by the lesson thus taught him, the king made his salutation and returned to his palace. The disciple also took his leave of his master and returned to the Himalayas. But the Bodhisatta continued to dwell on there, and, dying with Insight full and unbroken, was re-born in the Realm of Brahma.
His lesson ended, and the two stories told, the Master shewed the connexion linking them both together, and identified the Birth by saying,--"The Elder Bhaddiya was the disciple of those days, and I myself the master of the company of ascetics."
[Note. For the Introductory Story compare Cullavagga, VII. l. 5--.]
32:1 Cf. Oldenberg's Vinaya, Vol. in pp. 180-4 (translated at p. 232 of Vol. XX. of the Sacred Books of the East), for an account of the conversion of the six Sākyan princes and the barber Upāli.
32:2 No. 534 in Westergaard's list; not yet edited by Fausböll.