Shatapatha Brahmana 14.1.1.30

14.1.1.30

amṛnmayapāyī asti vā asyāṃ saṃsṛṣṭamiva yadasyāmanṛtam vadati tasmādamṛnmayadāyī

And whilst not drinking out of earthen (vessels); for whatever untruth (man) speaks on this (earth) is, as it were, immixed with her: therefore (one should do so) whilst not drinking out of earthen (vessels);