Garudapurana 1.50.59

1.50.59

ādāvoṅkāramuccārya namo 'nte tarpayāmi ca /
devānbrahmaṛṣīṃścaiva tarpayedakṣatodakaiḥ //

Uttering the syllable Oṃ at the beginning, followed by 'namaḥ' and 'tarpayāmi' at the end, / one should offer libations to the gods and the brahmanical sages with water mixed with unbroken grains;