Śatapatha Brāhmaṇa ("of a hundred paths") 2.2.1.1

2.2.1.1

uddhṛtyāhavanīyam pūrṇāhutiṃ juhoti | tadyatpūrṇāhutiṃ juhotyannādaṃ vā etamātmano janayate yadagniṃ tasmā etadannādyamapidadhāti yathā kumārāya vā jātāya vatsāya vā stanamapidadhyādevamasmā etadannādyamapidadhāti

When he has taken out the Âhavanîya fire, he performs the Full-offering. The reason why he performs the full-offering is that he thereby causes that Agni to become an eater of food for his own self; that he thereby offers food to him. Even as (a mother or cow) would offer the breast to a new-born child or calf, so does he thereby offer food to him.