Manava Dharmashastra 3.146

3.146

eṣām anyatamo yasya bhuñjīta śrāddham arcitaḥ
pitṝṇāṃ tasya tṛptiḥ syāc chāśvatī sāptapauruṣī //

If one of these three dines, duly honoured, at a funeral sacrifice, the ancestors of him (who gives the feast), as far as the seventh person, will be satisfied for a very long time.