Shrimad Bhagavad Gita As It Is -Shri Shrimad A.C Bhaktivedanta Swami Prabhupada
Chapter 6: Verse-13-14
In the rules of celibacy written by the great sage Yäjnavalkya it is said:
karmanä manasä väcä
“The vow of brahmacarya is meant to help one completely abstain from sex indulgence in work, words and mind—at all times, under all circumstances, and in all places.” No one can perform correct yoga practice through sex indulgence. Brahmacarya is taught, therefore, from childhood, when one has no knowledge of sex life. Children at the age of five are sent to the guru-kula, or the place of the spiritual master, and the master trains the young boys in the strict discipline of becoming brahmacäris. Without such practice, no one can make advancement in any yoga, whether it be dhyäna, jnäna or bhakti. One who, however, follows the rules and regulations of married life, having a sexual relationship only with his wife (and that also under regulation), is also called a brahmacäri. Such a restrained householder brahmacäri may be accepted in the bhakti school, but the jnäna and dhyäna schools do not even admit householder brahmacäris. They require complete abstinence without compromise. In the bhakti school, a householder brahmacäri is allowed controlled sex life because the cult of bhakti-yoga is so powerful that one automatically loses sexual attraction, being engaged in the superior service of the Lord. In the  it is said:
Whereas others are forced to restrain themselves from sense gratification, a devotee of the Lord automatically refrains because of superior taste. Other than the devotee, no one has any information of that superior taste. Vigata-bhih. One cannot be fearless unless one is fully in krsna consciousness. A conditioned soul is fearful due to his perverted memory, his forgetfulness of his eternal relationship with Krsna. The Bhägavatam says, bhayam dvitiyäbhinivesatah syäd isäd apetasya viparyayo ’smrtih.krsna consciousness is the only basis for fearlessness. Therefore, perfect practice is possible for a person who is krsna conscious. And since the ultimate goal of yoga practice is to see the Lord within, a krsna conscious person is already the best of all yogis. The principles of the yoga system mentioned herein are different from those of the popular so-called yoga societies.
- Bhagavad-gita 2.59