Mbh 3.135.5

“Lomasa said, ‘Knowing the determination of that high-souled sage, the sagacious Indra reflected and hit upon some expedient to dissuade him. Then Indra assumed the guise of an ascetic Brahmana, hundreds of years old, and infirm, and suffering from consumption. And he fell to throwing up a dam with sands, at that spot of the Bhagirathi to which Yavakri used to descend for performing ablutions. Because Yavakri, chief of the Brahmanas, paid no heed to Indra’s words, the latter began to fill the Ganga with sands. And without cessation, he threw handfuls of sand into the Bhagirathi, and began to construct the dam attracting the notice of the sage. And when that bull among the sages, Yavakri, saw Indra thus earnestly engaged in constructing the dam, he broke into laughter, and said the following words, ‘What art thou engaged in, O Brahmana, and what is thy object? Why dost thou, for nothing, make this mighty endeavour?’ Indra said, ‘I am trying, O my son, to dam the Ganga so that there may be a commodious passage. People experience considerable difficulty in crossing and recrossing (the river) by boat.’ Yavakri said, ‘O thou of ascetic wealth, thou canst not dam up this mighty current. O Brahmana, desist from, what is impracticable, and take up something that is practicable.’ Indra said, ‘O sage, I have imposed on myself this heavy task, even as, for obtaining a knowledge of the Vedas, thou hast begun these penances, which can never be fruitful.’ Yavakri said, ‘If, O chief of the celestials, those efforts of mine be fruitless, even as those of thy own, then, O lord of heavenly hosts, be thou pleased to do for me what is practicable. Vouchsafe unto me boons whereby I may excel other men.’