Vishnupurana 5.10.19

5.10.19

meghānāṃ payasāṃ ceśo devarājaḥ śatakratuḥ
tena saṃcoditā meghā varṣanty ambumayaṃ rasam //

At this season, when the skies were bright with stars, Krishńa, repairing to Vraja, found all the cowherds busily engaged in preparing for a sacrifice to be offered to Indra; and going to the elders, he asked them, as if out of curiosity, what festival of Indra it was in which they took so much pleasure. Nanda replied to his question, and said, "Śatakratu or Indra is the sovereign of the clouds and of the waters: sent by him, the former bestow moisture upon the earth, whence springs the grain, by which we and all embodied beings subsist; with which also, and with water, we please the gods: hence too these cows bear calves, and yield milk, and are happy, and well nourished. So when the clouds are seen distended with rain, the earth is neither barren of corn, nor bare of verdure, nor is man distressed by hunger. Indra, the giver of water, having drank the milk of earth by the solar ray, sheds it again upon the earth for the sustenance of all the world. On this account all sovereign princes offer with pleasure sacrifices to Indra at the end of the rains, and so also do we, and so do other people."