Shatapatha Brahmana 1.7.1.12

1.7.1.12

atha pavitraṃ nidadhati | tadvai prāṅnidadhyātprācī hi devānāṃ digatho udagudīcī hi manuṣyāṇāṃ digayaṃ vai pavitraṃ yo 'yam pavate so 'yamimāṃllokāṃstiryaṅṅanupavate tasmādudaṅnidadhyāt

He then puts the strainer (on the pot). He puts it down with the top turned eastwards, for the east is the region of the gods; or with the top turned northwards, for the north is the region of the men; means of purification (pavitram) assuredly is that (wind) which here blows, it sweeps across these worlds: let him therefore put it down with the front northwards.