SB 1.3.6

sa eva prathamaṁ devaḥ
 kaumāraṁ sargam āśritaḥ
cacāra duścaraṁ brahmā
 brahmacaryam akhaṇḍitam
Synonyms: 
saḥ — that; eva — certainly; prathamam — first; devaḥ — Supreme Lord; kaumāram — named the Kumāras (unmarried); sargam — creation; āśritaḥ — under; cacāra — performed; duścaram — very difficult to do; brahmā — in the order of Brahman; brahmacaryam — under discipline to realize the Absolute (Brahman); akhaṇḍitam — unbroken.
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.
Purport: 

The creation of the material world is effected, maintained and then again annihilated at certain intervals. So there are different names of the creations in terms of the particular types of Brahmā, the father of the living beings in the creation. The Kumāras, as above mentioned, appeared in the Kaumāra creation of the material world, and to teach us the process of Brahman realization, they underwent a severe type of disciplinary action as bachelors. These Kumāras are empowered incarnations. And before executing the severe type of disciplinary actions, all of them became qualified brāhmaṇas. This example suggests that one must first acquire the qualifications of a brāhmaṇa, not simply by birth but also by quality, and then one can undergo the process of Brahman realization.