Śatapatha Brāhmaṇa ("of a hundred paths") 3.1.3.11

3.1.3.11

yatra vai devāḥ | asurarakṣasāni jaghnustacuṣṇo dānavaḥ pratyaṅ patitvā manuṣyāṇāmakṣīṇi praviveśa sa eṣa kanīnakaḥ kumāraka iva paribhāsate tasmā evaitadyajñamupaprayantsarvato 'śmapurām paridadhātyaśmā hyāñjanam

Now, when the gods slew the Asura-Rakshas, Sushna, the Dânava, falling backward entered into the eyes of men: he is that pupil of the eye, and looks like a young lad. Against him he (the sacrificer), now that he enters on the sacrifice, raises a rampart of stone all round himself, for the ointment is (produced from) stone.