Srimad Bhagavatam Canto 03, Chapter 12, Text 42

SB 3.12.42

savitram prajapatyam ca
 brahmam catha brhat tatha
varta sañcaya-salina-
 siloñcha iti vai grhe
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Then the thread ceremony for the twice-born was inaugurated, as were the rules to be followed for at least one year after acceptance of the Vedas, rules for observing complete abstinence from sex life, vocations in terms of Vedic injunctions, various professional duties in household life, and the method of maintaining a livelihood without anyone’s cooperation by picking up rejected grains.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
During student life the brahmacaris were given full instructions about the importance of the human form of life. Thus the basic education was designed to encourage the student in becoming free from family encumbrances. Only students unable to accept such a vow in life were allowed to go home and marry a suitable wife. Otherwise, the student would remain a permanent brahmacari, observing complete abstinence from sex life for his whole life. It all depended on the quality of the student’s training. We had the opportunity to meet an avowed brahmacari in the personality of our spiritual master, Om Visnupada Sri Srimad Bhaktisiddhanta Gosvami Maharaja. Such a great soul is called a naisthika-brahmacari.
Srimad Bhagavatam Canto 03, Chapter 12, Text 41
Srimad Bhagavatam Canto 03, Chapter 12, Text 43