Anandakanda 2.4.20

2.4.20

taptaṃ taptaṃ tridhā siñcyācchuddhimāyāti niścayam /
gomūtreṇa pacedyāmaṃ tāmrapātraṃ dṛḍhāgninā //

Heated repeatedly, one should quench it three times; it certainly attains purification. / One should cook a copper vessel with cow's urine for one watch over a strong fire;