Anandakanda 2.4.29

2.4.29

ācchādya dhūrtapatraistu ruddhvā gajapuṭe pacet /
svāṅgaśītaṃ tataścūrṇaṃ mṛtaṃ bhavati niścitam //

Having covered it with datura leaves and sealed it, one should cook it in an elephant-pit incineration. / The powder, cooled of its own accord, then certainly becomes killed.