Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.1.22

1.3.1.22

prokṣaṇīṣu pavitre bhavataḥ | te tata ādatte tābhyāmājyamutpunātyeko vā utpavanasya bandhurmedhyamevaitatkaroti

The two strainers are lying in the sprinkling water. He takes them from thence and purifies (ut-pû) the butter with them. Now one of them is related to the wind (that blows) upwards (utpavana), so that he thereby makes it (the butter) sacrificially pure.