Śatapatha Brāhmaṇa ("of a hundred paths") 6.5.4.16

6.5.4.16

ajāyai payasācṛṇatti | prajāpatervai śokādajā samabhavanprajāpatiragnirno vā ātmātmānaṃ hinastyahiṃsāyai yadvevājāyā ajā ha sarvā oṣadhīratti sarvāsāmevaināmetadoṣadhīnāṃ rasenācṛṇatti

He pours goat's milk into it to avoid injury; for the goat sprang from Pragâpati's head, and Pragâpati is Agni; and one does not injure one's own self. And as to why it is goat's (milk),--the goat eats all (kinds of) herbs: he thus pours into it (the pan) the sap of all (kinds of) herbs.