SB 9.4.30
vratante kartike masi
tri-ratram samupositah
snatah kadacit kalindyam
harim madhuvane ’rcayat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In the month of Kartika, after observing that vow for one year, after observing a fast for three nights and after bathing in the Yamuna, Maharaja Ambarisa worshiped the Supreme Personality of Godhead, Hari, in Madhuvana.