Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.1.13

3.6.1.13

atha yāḥ prokṣaṇyaḥ pariśiṣyante | tā avaṭe 'vanayati śundhantāṃ lokāḥ pitṛṣadanā iti pitṛdevatyo vai kūpaḥ khātastamevaitanmedhyaṃ karoti

And the sprinkling-water which remains he pours into the hole, with, 'Be the worlds pure wherein the Fathers reside!' for a pit that is dug is sacred to the Fathers: this he thereby renders sacrificially pure.