The Compendium of Caraka 6.5.138

6.5.138

pariveṣṭya pradīptāṃstu balvajānathavā kuśān/
bhiṣakkumbhe samāvāpya gulmaṃ ghaṭamukhe nyaset//

Wrapping burning balvaja or kuśa grass [inside a vessel],
the physician, having placed it in an earthen jar, should set the mouth of the jar over the lump.