Revākhaṇḍa of the Skandapurāṇa manuscripts (RKS) 76.61

76.61

dadate toyam āspṛśya so 'gniṣṭomaphalaṃ labhet /
aṣṭamyāṃ ca caturdaśyāṃ pūjayec ca viśeṣataḥ //

touching the water, he obtains the fruit of an agniṣṭoma sacrifice.
One should worship especially on the eighth and fourteenth lunar days;