Chandogya Upanishad
Prapathaka V, Khanda 21
'And he who offers the third oblation, should offer it to Apâna (down-breathing), saying Svâhâ. Then Apâna is satisfied. If Apâna is satisfied, the tongue is satisfied, if the tongue is satisfied, Agni (fire) is satisfied, if Agni is satisfied, the earth is satisfied, if the earth is satisfied, whatever is under the earth and under fire is satisfied.