Agni Purana 263.23

263.23

pitre tu prathamaṃ dadyāttatpitre tadanantaram /
prapitāmahāya tanmātre pitṛmātre tato 'rpayet //

He should give first to the father, immediately after to his father, / [then] to the paternal great-grandfather, then offer to his mother, [and] to the father's mother;