Apastambasmriti 7.6

7.6

trirātramupavāsaḥ syātpañcagavyaṃ viśodhanam
niśāṃ prāpya tu tāṃ yoniṃ prajākārañca kārayet

There shall be fasting for a period of three nights, and pañcagavya is the purifier; / having reached that night, he should engage with the womb to produce offspring.