The Compendium of Bheḷa 4.5.5

4.5.5

tryahantu[-ha] khalu purāṇarudhiraṃ parivarjayet | kiñ ca tatpurāṇam? yadāditastryahaṃ parisravadṛtukāle tatpurāṇam | tasmin tryahe garbha-upakramaṇe[upakrameṇa] na tiṣṭhati | avasthito[avasthi vā] vā nāyuṣi samartho bhavati | nirgate[nirgave] tu tryaheṇa purāṇe rudhirecāvasthite[ṇa] śuddhasnātāyāścaturthaṣaṣṭha-aṣṭama[aṣṭa]-daśama-dvādaśeṣu[dvādaśamu] ahassu garbhovakramamāṇaḥ pumān bhavati | pañcamasaptama-navamaikādaśeṣu[-navaikādaśu] strītvāyopakalpate |sa eṣa āsaptarātrātsarvasañcāro ' bhidadhatyataḥ paramasañcārovakṛtatvād vālpāt? ||

One should indeed avoid the old blood for three days. And what is that old [blood]? That which flows from the beginning for three days at the fertile period, that is old. During those three days, when conception is attempted, the fetus does not stay; or if it stays, it is not capable of long life. But when the old blood has exited after three days and has ceased, for a woman who has bathed clean, the fetus entering on the fourth, sixth, eighth, tenth, and twelfth days becomes male. On the fifth, seventh, ninth, and eleventh [days], it develops toward femaleness. This intercourse of all [sorts] is said [to be suitable] up to seven nights; beyond this, intercourse [is forbidden] due to impairment or deficiency.