Garudapurana 1.84.27

1.84.27

sa tatphalamavāpnoti kṛtvā śrāddhaṃ gayāśire /
śamīpatrapramāṇena piṇḍaṃ dadyādgayāśire //

he obtains that same reward by performing śrāddha at Gayāśira.
One should offer a piṇḍa the size of a śamī leaf at Gayāśira;