Śatapatha Brāhmaṇa ("of a hundred paths") 3.4.4.24

3.4.4.24

atha juhoti | yayā dvirekasyāhnaḥ pracariṣyanbhavati yā te agne rajaḥśayā tanūrvarṣiṣṭhā gahvareṣṭhā ugraṃ vaco apāvadhīttveṣaṃ vaco apāvadhītsvāhetyevaṃrūpā hi sāsīdrajatā hi sāsīt

Again he offers (with the verse) with which he will have to perform twice in one day, 'What most excellent silver-clad body is thine, O Agni, established in the deep, it hath chased away the cruel word, it hath chased away the fearful word; Hail!' for such-like it was, it was indeed silver.