Matsyapurana 7.60

7.60

nūnam etat pariṇatam adhunā kṛṣṇapūjanāt
vajreṇāpi hatāḥ santo na vināśam avāpnuyuḥ //

Indra came to know, through His Yogic powers, that it was on account of Diti’s observance of the Dvâdaśî fast and worship of Kâma that His weapon could not destroy her child in the womb. His own thoughts began to oppress Him. He said to Himself that, instead of one, they multiplied into forty-nine. Devas could not destroy them. It would be safer to make them Devas.—59-61.