The Law Code of Devala 14

14

tadā'sau tu kuṭumbānāṃ paṅktie prāpnoti nānyathā
svabhāyāṃ ca yathānyāyaṃ gacchanneva viśudhyati

Then indeed he enters into the row of his kin, not otherwise; / and approaching his own wife according to rule, he becomes pure.