SB 9.11.11

antarvatny āgate kāle
 yamau sā suṣuve sutau
kuśo lava iti khyātau
 tayoś cakre kriyā muniḥ
Synonyms: 
antarvatnī — the pregnant wife; āgate — arrived; kāle — in due course of time; yamau — twins; — Sītādevī; suṣuve — gave birth to; sutau — two sons; kuśaḥ — Kuśa; lavaḥ — Lava; iti — thus; khyātau — celebrated; tayoḥ — of them; cakre — performed; kriyāḥ — the ritualistic ceremonies of birth; muniḥ — the great sage Vālmīki.
Translation: 
When the time came, the pregnant mother Sītādevī gave birth to twin sons, later celebrated as Lava and Kuśa. The ritualistic ceremonies for their birth were performed by Vālmīki Muni.