Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.4.7

4.2.4.7

taṃ śasyamāne 'vanayati | tadenaṃ dvādaśaṃ stotramatinayati tathā paramparamāyuḥ samaśnute tatho ha yajamāno jyogjīvati tasmādbrāhmaṇo 'gniṣṭomasatsyādaitasya homānna sarpenna prasrāvayeta tathā sarvamāyuḥ samaśnuta āyurvā asyaiṣa tathā sarvamāyureti

He pours it out during the recitation of the sastra; whereby he guides him safely over the twelvefold chant of praise: thus he obtains ever continued life, and thus does the sacrificer live long. Therefore the Brâhman should sit through the praise of Agni (Agnishtoma); till the offering of this (libation) he must not slip away --nor must he discharge urine: thus he obtains the full life--for this (libation) is his life--thus he reaches the full (measure of) life.