Śatapatha Brāhmaṇa ("of a hundred paths") 1.1.1.3

1.1.1.3

atha saṃsthite visṛjate | agne vratapate vratamacāriṣaṃ tādaśakam tanme rādhītyaśakadyetadyo yajñasya saṃsthāmagannarādhi hyasmai yo yajñasya saṃsthāmagannetena nveva bhūyiṣṭhā iva vratamupayantyanena tvevopeyāt

After the completion (of the sacrifice) he divests himself (of the vow), with the text (Vâg. S. II, 28 a), 'O Agni, Lord of Vows! I have kept the vow; I have been equal to it; I have succeeded in it;' for he who has attained the completion of the sacrifice, has indeed been equal to it; and he who has attained the completion of the sacrifice, has succeeded in it. It is in this way that most (sacrificers) will probably enter on the vow; but one may also enter on it in the following way.