Garudapurana 1.218.11

1.218.11

tataḥ pitṛpitāmahaprapitāmahānāṃ mātāmahapramātāmahavṛddhapramātāmahānāṃ sapatnīkānāṃ śrāddhamahaṃ kariṣye iti anujñāvacanam /
kuruṣveti brāhmaṇairukte /
oṃ devatābhyaḥ pitṛbhyaśca- ititrirjapet //

Then the words requesting permission [are spoken]: "I shall perform the śrāddha of the fathers, grandfathers, and great-grandfathers, and of the maternal grandfathers, maternal great-grandfathers, and maternal great-great-grandfathers, together with their wives." / When the brāhmaṇas reply, "Perform [it]," / he should mutter three times: "Om, to the deities and to the ancestors..."