Agniveshyagrihyasutra 2.7.1.6

2.7.1.6

etaiścānyaiśca nimittāni bhavanti cet pūrvapakṣe puṇye nakṣatre gomayena gocarmamātraṃ sthaṇḍilamupalipya yamaniyamayantraiḥ vratopavāsaiśca prāyaścittaṃ kṛtvā agnimupasamādhāya samparistīryā daṇḍapradānāt pūrvavadupanayanaṃ kṛtvā sāvitrīṃ vācayati

If there are these and other occasions, having smeared an area of sacrificial ground measuring a cow-hide with cow-dung in the bright half of the month under an auspicious constellation, having performed an expiation with the restraints, observances, ascetic disciplines, and fasts, having laid the fire, having strewn [darbha grass] around, having performed the initiatory investiture as before up to the giving of the staff, he causes [him] to recite the Sāvitrī verse.