Shiva Purana
धर्मपत्न्यास्तु गमनं गृहस्थस्य विधीयते ॥ ब्रह्मचर्यं वनस्थानां यतीनां ब्रह्मचारिणाम् ॥ १८ ॥
Sexual approach only to one’s own wife duly wed is prescribed for a householder and celibacy for all the other three, viz. Brahmacārins, Vānaprasthas and Sannyāsins.
english translation
dharmapatnyAstu gamanaM gRhasthasya vidhIyate ॥ brahmacaryaM vanasthAnAM yatInAM brahmacAriNAm ॥ 18 ॥
hk transliteration by Sanscript