Srimad Bhagavatam Canto 04, Chapter 08, Text 01

SB 4.8.1

maitreya uvaca
sanakadya naradas ca
rbhur hamso ’runir yatih
naite grhan brahma-suta
hy avasann urdhva-retasah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The great sage Maitreya said: The four great Kumara sages headed by Sanaka, as well as Narada, Rbhu, Hamsa, Aruni and Yati, all sons of Brahma, did not live at home, but became urdhva-reta, or naisthika-brahmacaris, unadulterated celibates.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The system of brahmacarya has been current since the birth of Brahma. A section of the population, especially male, did not marry at all. Instead of allowing their semen to be driven downwards, they used to lift the semen up to the brain. They are called urdhva-retasah, those who lift up. Semen is so important that if, by the yogic process, one can lift the semen up to the brain, he can perform wonderful work — one’s memory is enabled to act very swiftly, and the duration of life is increased. Yogis can thus perform all kinds of austerity with steadiness and be elevated to the highest perfectional stage, even to the spiritual world. Vivid examples of brahmacaris who accepted this principle of life are the four sages Sanaka, Sanandana, Sanatana and Sanat-kumara, as well as Narada and others.
Another significant phrase here is naite grhan hy avasan, “they did not live at home.” Grha means “home” as well as “wife.” In fact, “home” means wife; “home” does not mean a room or a house. One who lives with a wife lives at home; otherwise, a sannyasi or brahmacari, even though he may live in a room or in a house, does not live at home. That they did not live at home means that they did not accept a wife, and so there was no question of their discharging semen. Semen is meant to be discharged when one has a home, a wife and the intention to beget children; otherwise there is no injunction for discharging semen. These principles were followed from the beginning of creation, and such brahmacaris never created progeny. This narration has dealt with the descendants of Lord Brahma from Manu’s daughter Prasuti. Prasuti’s daughter was Daksayani, or Sati, in relation to whom the story of the Daksa yajña was narrated. Maitreya is now explaining about the progeny of the sons of Brahma. Out of the many sons of Brahma, the brahmacari sons headed by Sanaka and Narada did not marry at all, and therefore there is no question of narrating the history of their descendants.
Srimad Bhagavatam Canto 04, Chapter 08, Text 02