Brihadaranyaka Upanishad 5.14.8

5.14.8

etaddha vai tajjanako vaideho buḍilamāśvatarāśvimuvāca yannu ho tadgāyatrībidabrūthā atha katham̐ hastībhūto vahasīti mukham̐hyasyāḥ samrāṇna vidāṃ cakāreti hovāca tasyā agnireva mukhaṃ yadi ha vā api bahvivāgnāvabhyādadhati sarvameva tatsaṃdahatyevam̐ haivaivaṃvidyadyapi bahviva pāpaṃ kurute sarvameva tatsaṃpsāya śuddhaḥ pūto'jaro'mṛtaḥsaṃbhavati

On this Janaka, Emperor of Videha, is said to have told Budila, the son of Ashwatarâshwa, 'Well, you gave yourself out as a knower of the Gâyatri; then why, alas, are you carrying (me) as an elephant?' He replied, 'Because I did not know its mouth, O Emperor.' 'Fire is its mouth. Even if they put a large quantity of fuel into the fire, it is all burnt up. Similarly, even if one who knows as above commits a great many sins, he consumes them all and becomes pure, cleansed, undecaying and immortal.'

5.14.8.p1

iti pañcamādhyāye caturdaśaṃ brāhmaṇam