Vow (SB cantos 1 - 4)
Appearance
Srimad-Bhagavatam
SB Canto 1
SB 1.3.6, Translation:
First of all, in the beginning of creation, there were the four unmarried sons of Brahmā (the Kumāras), who, being situated in a vow of celibacy, underwent severe austerities for realization of the Absolute Truth.