SB 9.1.21

evaṁ vyavasito rājan
 bhagavān sa mahā-yaśāḥ
astauṣīd ādi-puruṣam
 ilāyāḥ puṁstva-kāmyayā
Word for word: 
evam — thus; vyavasitaḥ — deciding; rājan — O King Parīkṣit; bhagavān — the most powerful; saḥ — Vasiṣṭha; mahā-yaśāḥ — very famous; astauṣīt — offered prayers; ādi-puruṣam — unto the Supreme Person, Lord Viṣṇu; ilāyāḥ — of Ilā; puṁstva-kāmyayā — for the transformation into a male.
Translation: 
Śukadeva Gosvāmī said: O King Parīkṣit, after the most famous and powerful Vasiṣṭha made this decision, he offered prayers to the Supreme Person, Viṣṇu, to transform Ilā into a male.