Mahabharata 1.99.38

1.99.38

bhrātuḥ putrānpradāsyāmi mitrāvaruṇayoḥ samān |
vrataṃ caretāṃ te devyau nirdiṣṭamiha yanmayā || 38 ||

"Vyasa, hearing this, said, 'O Satyavati, thou knowest what virtue is both in respect of this life and the other. O thou of great wisdom, thy affections also are set on virtue. Therefore, at thy command, making virtue my motive, I shall do what thou desirest. Indeed, this practice that is conformable to the true and eternal religion is known to me, I shall give unto my brother children that shall be like unto Mitra and Varuna. Let the ladies then duly observe for one full year the vow I indicate. They shall then be purified. No women shall ever approach me without having observed a rigid vow.'