Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.24

3.2.2.24

atha yaddīkṣitaḥ | avratyaṃ vā vyāharati krudhyati vā tanmithyākaroti vratam pramīṇātyakrodho hyeva dīkṣitasyāgnirvai devānāṃ vratapatistamevaitadupadhāvati tvamagne vratapā asi deva ā martyeṣvā tvāṃ yajñaṣvīḍya iti tasyo haiṣā prāyaścittistatho hāsyaitanna mithyākṛtam bhavati na vratam pramīṇāti tasmādāha tvamagne vratapā asi deva ā martyeṣvā tvaṃ yajñaṣvīḍya iti

For, when he who is consecrated utters anything that is foreign to the vow, or when he becomes angry, he commits a fault and breaks his vow, since suppression of anger behoves him who is consecrated. Now, Agni is the Lord of vows among the gods,--it is to him therefore that he resorts (Vâg. S. IV, 16; Rig-veda VIII, II, 7): 'Thou, O Agni, art the divine guardian of vows among men, to whom praise is due at the sacrifices.' This, then, is his atonement for that (transgression); and thus that fault is not committed by him, and he does not break his vow: therefore he says, 'Thou, O Agni, art the divine guardian of vows among men, to whom praise is due at the sacrifices.'