The Law Code of Yājñavalkya 1.3.80

1.3.80

aputrām alabdhaputrāṃ pitrādibhiḥ putrārtham anujñāto devaro bhartuḥ kanīyān bhrātā sapiṇḍo vā uktalakṣaṇaḥ sagotraḥ vā | eteṣāṃ pūrvasyābhāve paraḥ paraḥ ghṛtābhyaktasarvāṅgaḥ ṛtāv eva vakṣyamāṇalakṣaṇe iyād gacched ā garbhotpatteḥ | ūrdhvaṃ punar gacchan anyena vā prakāreṇa tadā patito bhavati | anena vidhinotpannaḥ pūrvapariṇetuḥ kṣetrajaḥ putro bhavet | etac ca vāgdattāviṣayam ity ācāryāḥ,

"A sonless woman" means one who has not obtained a son. "Authorized" by her father and others for the sake of obtaining a son, "the husband's brother" is the younger brother of the husband; or a sapiṇḍa conforming to the stated definition; or a sagotra. In the absence of the former of these, each subsequent one [is eligible]. Having anointed his entire body with clarified butter, he may approach—go to—her only in the fertile period that has the characteristics to be stated later, until conception occurs. Going to her beyond that, or in another manner, he becomes an outcaste. A son produced by this rule shall be the field-born son of the previous husband who married her. And the teachers maintain that this applies [only] to a betrothed maiden,