Garudapurana 1.48.75

1.48.75

svaśāstravihitairmantraiḥ praṇavenātha homayet /
tataḥ pūrṇāhutiṃ dattvā pūrṇātpūrṇamanārethaḥ //

he should make oblations with the mantras prescribed by his own scripture or with the Praṇava; / then, having offered the full oblation, [saying] "pūrṇāt pūrṇam..." [without selfish ends];