The Prashna Upanishad with Shankara’s Commentary
तद्ये ह वै तत्प्रजापतिव्रतं चरन्ति ते मिथुनमुत्पादयन्ते । तेषामेवैष ब्रह्मलोको येषां तपो ब्रह्मचर्यं येषु सत्यं प्रतिष्टितम् ॥ १५ ॥
tadye ha vai tatprajāpativrataṃ caranti te mithunamutpādayante | teṣāmevaiṣa brahmaloko yeṣāṃ tapo brahmacaryaṃ yeṣu satyaṃ pratiṣṭitam || 15 ||
15. Thus, those who follow the vow of the lord of creation produce couples. To them alone, is this Brahmalôka, in whom tapas, brahmacharyam and truth abide.
Com.—Thus, this being so. Of those householders (Vai and Ha are two particles, remembrances of well-known things), who obey the vow of Prajâpati (lord of creation), i.e., who approach their wives in due season, their visible fruits (in this world) is this. What? They produce a couple, i.e., son and daughter. The invisible fruits (pertaining to the future world) are also to them alone, performing sacrificial and pious acts and making gifts. This Brahmalôka, i.e., the world of the moon, to which the route of the manes leads, is to those in whom tapas, i.e., the vow of a snâtaka, etc., Brahmacharyam, i.e., abstinence from sexual intercourse except in season, and truth, i.e., abstinence from falsehood abide always without any deviation.