Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 13
Sanskrit:
अप्रजस्य मनो: पूर्वं वसिष्ठो भगवान् किल ।मित्रावरुणयोरिष्टिं प्रजार्थमकरोद् विभु: ॥ १३ ॥
ITRANS:
aprajasya manoḥ pūrvaṁvasiṣṭho bhagavān kilamitrā-varuṇayor iṣṭiṁprajārtham akarod vibhuḥ
Translation:
Manu at first had no sons. Therefore, in order to get a son for him, the great saint Vasiṣṭha, who was very powerful in spiritual knowledge, performed a sacrifice to satisfy the demigods Mitra and Varuṇa.