Śatapatha Brāhmaṇa ("of a hundred paths") 3.4.4.25

3.4.4.25

atha juhoti | yayādvirekasyāhnaḥ pracariṣyanbhavati yā te agne hariśayā tanūrvarṣiṣṭhā ugraṃ vaco apāvadhīttveṣaṃ vaco apāvadhītsvāhetyevaṃrūpā hi sāsīddhariṇī hi sāsīdyadyu dvādaśopasada upeyāccaturahamekayā pracareccaturahamekayā

And again he offers (with the verse) with which he will have to perform twice in one day, 'What most excellent gold-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 golden. If he undertakes twelve Upasads, let him perform each of them for four days.