Shatapatha Brahmana 1.3.3.16

1.3.3.16

tatheti devā abruvan | yadbahiṣparidhi skantsyati tadyuṣmāsu hutamatha yadva uparyupari hoṣyanti tadvo 'viṣyatīti sa yadagnau juhvati tadenānavatyatha yadenānuparyupari juhvati tadenānavatyatham yadbahiṣparidhi skandati tadeteṣu hutaṃ tasmādu ha nāga iva skannaṃ syādimāṃ vai te prāviśanyadvā idaṃkiṃca skandatyasyāmeva tatsarvam pratitiṣṭhati

The gods said: 'So be it! What shall fall outside the enclosure, that is offered unto you; and what they shall offer just upon you, that will sate you; and what they shall offer up in the fire that will sate you!' Thus what they offer up in the fire, that satisfies them (the Agnis); and what they offer up just upon them (the enclosing-sticks, or Agnis), that satisfies them; and what is spilled outside the enclosure, that is offered to them: hence no sin attaches to what (butter) is spilt; for into this earth they entered (when they, the Agnis, passed away), and whatever is spilt here,--all that remains indeed in her.