Shankhayanagrihyasutra 2.10.8

2.10.8

: (.sauparṇa vrata bhāṣitam dṛṣṭam vṛddha sampradāya anuṣṭhitam tryāyuṣam pañcabhir mantraiḥ pratimantram lalāṭe hṛdaye dakṣiṇa skandhe vāme ca tataḥ pṛṣṭhe ca pañcasu bhasmanā tripuṇḍhram karoto.)/

He who approaches the fire after having sacrificed thus, studies of these Vedas, one, two, three, or all.

2.10.8.p1

: sa eteṣām vedānām ekam dvau trīn sarvān vā adhīte ya evam hutvā agnim upatiṣṭhate /