The Jataka, Volume I, tr. by Robert Chalmers, , at sacred-texts.com
"Pajjunna, thunder!"--This story the Master told while at Jetavana, about the rain he caused to fall. For in those days, so it is said, there fell no rain in Kosala; the crops withered; and everywhere the ponds, tanks, and lakes dried up. Even the pool of Jetavana by the embattled gateway of Jetavana gave out; and the fish and tortoises buried themselves in the mud. Then came the crows and hawks with their lance-like beaks, and busily picked them out writhing and wriggling, and devoured them.
As he marked how the fishes and the tortoises were being destroyed, the Master's heart was moved with compassion, and he exclaimed,--"This day  must I cause rain to fall." So, when the night grew day, after attending to his bodily needs, he waited till it was the proper hour to go the round in quest of alms, and then, girt round by a host of the Brethren, and perfect with the perfection of a Buddha, he went into Sāvatthi for alms. On his way back to the monastery in the afternoon from his round for alms in Sāvatthi, he stopped upon the steps leading down to the tank of Jetavana, and thus addressed the Elder
Ānanda:--"Bring me a bathing-dress, Ānanda; for I would bathe in the tank of Jetavana." "But surely, sir," replied the Elder, "the water is all dried up, and only mud is left." "Great is a Buddha's power, Ānanda. Go, bring me the bathing-dress," said the Master. So the Elder went and brought the bathing-dress, which the Master donned, using one end to go round his waist, and covering his body up with the other. So clad, he took his stand upon the tank-steps, and exclaimed,--"I would fain bathe in the tank of Jetavana."
That instant the yellow-stone throne of Sakka grew hot beneath him, and he sought to discover the cause. Realising what was the matter, he summoned the King of the Storm-Clouds, and said, "The Master is standing on the steps of the tank of Jetavana, and wishes to bathe. Make haste and pour down rain in a single torrent over all the kingdom of Kosala." Obedient to Sakka's command, the King of the Storm-Clouds clad himself in one cloud as an under garment, and another cloud as an outer garment, and chaunting the rain-song 1, he darted forth eastward. And lo! he appeared in the east as a cloud of the bigness of a threshing-floor, which grew and grew till it was as big as a hundred, as a thousand, threshing-floors; and he thundered and lightened, and bending down his face and mouth deluged all Kosala with torrents of rain. Unbroken was the downpour, quickly filling the tank of Jetavana, and stopping only when the water was level with the topmost step. Then the Master bathed in the tank, and coming up out of the water donned his two orange-coloured cloths and his girdle, adjusting his Buddha-robe around him so as to leave one shoulder bare. In this guise he set forth, surrounded by the Brethren, and passed into his Perfumed Chamber, fragrant with sweet-smelling flowers. Here on the Buddha-seat he sate, and when the Brethren had performed their duties, he rose and exhorted the Brotherhood from the jewelled steps of his throne, and dismissed them from his presence. Passing now within his own sweet-smelling odorous chamber, he stretched himself, lion-like, upon his right side.
At even, the Brethren gathered together in the Hall of Truth, and dwelt on the forbearance and loving-kindness of the Master. "When the crops were withering, when the pools were drying up, and the fishes and tortoises were in grievous plight, then did he in his compassion come forth as a saviour. Donning a bathing-dress, he stood on the steps of the tank of Jetavana, and in a little
space made the rain to pour down from the heavens till it seemed like to overwhelm all Kosala with its torrents. And by the time he returned to the Monastery, he had freed all alike from their tribulations both of mind and body."
 So ran their talk when the Master came forth from his Perfumed Chamber into the Hall of Truth, and asked what was their theme of conversation; and they told him. "This is not the first time, Brethren," said the Master, "that the Blessed One has made the rain to fall in the hour of general need. He did the like when born into the brute-creation, in the days when he was King of the Fish." And so saying, he told this story of the past:--
Once on a time, in this selfsame kingdom of Kosala and at Sāvatthi too, there was a pond where the tank of Jetavana now is,--a pond fenced in by a tangle of climbing plants. Therein dwelt the Bodhisatta, who had come to life as a fish in those days. And, then as now, there was a drought in the land; the crops withered; water gave out in tank and pool; and the fishes and tortoises buried themselves in the mud. Like-wise, when the fishes and tortoises of this pond had hidden themselves in its mud, the crows and other birds, flocking to the spot, picked them out with their beaks and devoured them. Seeing the fate of his kinsfolk, and knowing that none but he could save them in their hour of need, the Bodhisatta resolved to make a solemn Profession of Goodness, and by its efficacy to make rain fall from the heavens so as to save his kinsfolk from certain death. So, parting asunder the black mud, he came forth,--a mighty fish, blackened with mud as a casket of the finest sandal-wood which has been smeared with collyrium. Opening his eyes which were as washen rubies, and looking up to the heavens he thus bespoke Pajjunna, King of Devas,--"My heart is heavy within me for my kinsfolk's sake, my good Pajjunna. How comes it, pray, that, when I who am righteous am distressed for my kinsfolk, you send no rain from heaven? For I, though born where it is customary to prey on one's kinsfolk, have never from my youth up devoured any fish, even of the size of a grain of rice; nor have I ever robbed a single living creature of its life. By the truth of this my Protestation, I call upon you to send rain and succour my kinsfolk." Therewithal, he called to Pajjunna, King of Devas, as a master might call to a servant, in this stanza:--
[paragraph continues] In such wise, as a master might call to a servant, did the Bodhisatta call to Pajjunna, thereby causing heavy rains to fall and relieving numbers from the fear of death. And when his life closed, he passed away to fare according to his deserts.
"So this is not the first time, Brethren," said the Master, "that the Blessed One has caused the rain to fall. He did the like in bygone days, when he was a fish." His lesson ended, he identified the Birth by saying, "The Buddha's disciples were the fishes of those days, Ānanda was Pajjunna, King of Devas, and I myself the King of the Fish."
[Note. Cf. Cariyā-piṭaka (P. T. S. edition) page 99.]
183:1 In the J. R. A. S. (New Series) 12, 286, is given a Megha-sūtra.