Vayupurana 2.14.42

Vāyupurāṇa 2.14.42

ataḥ paraṃ vidhiṃ saumyaṃ bhuktavatsu dvijātiṣu.
ānupūrvyeṇa vidhinā tanme nigadataḥ śrṛṇu .. 14.40 ..