Revākhaṇḍa ascribed to the Vāyupurāṇa (RKV) 70.3

70.3

ṣaṣṭhyāṃṣaṣṭhyāṃ nṛpaśreṣṭha hyaṣṭamyāṃ ca caturdaśīm /
snānaṃ yaḥ kārayenmartyaḥ śrāddhaṃ preteṣu bhaktitaḥ /
tasya pāpakṣayaḥ pārtha sūryaloke mahīyate //

Whoever takes a sacred bath on every sixth day, on the eighth, and on the fourteenth, O best of kings, / and performs a funeral offering for the ancestors with devotion, / his sin is destroyed, O son of Pṛthā, and he is honored in the world of Sūrya.