SB 9.9.38
ata urdhvam sa tatyaja
stri-sukham karmanaprajah
vasisthas tad-anujñato
madayantyam prajam adhat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
After being thus instructed, the King gave up the future happiness of sexual intercourse and by destiny remained sonless. Later, with the King’s permission, the great saint Vasistha begot a child in the womb of Madayanti.