Srimad Bhagavatam Canto 11, Chapter 18, Text 43

SB 11.18.43

brahmacaryam tapah saucam
 santoso bhuta-sauhrdam
grhasthasyapy rtau gantuh
 sarvesam mad-upasanam
A householder may approach his wife for sex only at the time prescribed for begetting children. Otherwise, the householder should practice celibacy, austerity, cleanliness of mind and body, satisfaction in his natural position, and friendship toward all living entities. Worship of Me is to be practiced by all human beings, regardless of social or occupational divisions.
Sarvesam mad-upasanam indicates that all followers of the varnasrama system must worship Lord Krsna or risk falling down from their position. As stated in Srimad-Bhagavatam (11.5.3), na bhajanty avajananti sthanad bhrastah patanty adhah: even though one may be advanced in the performance of Vedic rituals and customs, without worshiping the Supreme Lord one will certainly fall down.
Those in the householder asrama are not authorized to enjoy life like pigs and dogs, freely exercising their sexual potency. A religious householder should approach his wife at the prescribed time and place and beget a saintly child for the pleasure of the Supreme Lord. Otherwise, it is specifically mentioned here that a householder must practice celibacy along with all of the other members of advanced human civilization. The word saucam indicates cleanliness of mind and body, or else freedom from attachment and repulsion. One who faithfully worships God as the supreme controller experiences santosa, full satisfaction in whatever situation the Lord arranges. By seeing Lord Krsna within everyone, one becomes bhuta-suhrt, the well-wishing friend of all.
Srimad Bhagavatam Canto 11, Chapter 18, Text 40-41
Srimad Bhagavatam Canto 11, Chapter 18, Text 44