Shatapatha Brahmana 8.5.1.6

8.5.1.6

yadvevaitā asapatnā upadadhāti | etadvai prajāpatimetasminnātmanaḥ pratihite sarvataḥ pāpmopāyatata sa etā iṣṭakā apaśyadasapatnāstā upādhatta tābhistam pāpmānamapāhata pāpmā vai sapatnastadyadetābhiḥ pāpmānaṃ sapatnamapāhata tasmādetā asapatnāḥ

And as to why he lays down those Asapatnâs. Now at that time, when that (part) of his body had been restored, evil beset Pragâpati on every side. He saw those foeless bricks, and laid them down, and by means of them he drove off evil, for foe means evil; and because, by means of them he drove off the foe, evil, therefore they are (called) 'foeless' (bricks).