Chandogya Upanishad 4.17

Pragâpati brooded over the worlds, and from them thus brooded on he squeezed out the essences, Agni (fire) from the earth, Vâyu (air) from the sky, Âditya (the sun) from heaven.

He brooded over these three deities, and from them thus brooded on he squeezed out the essences, the Rik verses from Agni, the Yagus verses from Vâyu, the Sâman verses from Âditya.

He brooded over the threefold knowledge (the three Vedas), and from it thus brooded on he squeezed out the essences, the sacred interjection Bhûs from the Rik verses, the sacred interjection Bhuvas from the Yagus verses, the sacred interjection Svar from the Sâman verses.

If the sacrifice is injured from the Rig-veda side, let him offer a libation in the Gârhapatya fire, saying, Bhûh, Svâha! Thus does he bind together and heal, by means of the essence and the power of the Rik verses themselves, whatever break the Rik sacrifice may have suffered.

If the sacrifice is injured from the Yagur-veda side, let him offer a libation in the Dakshina fire, saying, Bhuvah, Svâhâ! Thus does he bind together and heal, by means of the essence and the power of the Yagus verses themselves, whatever break the Yagus sacrifice may have suffered.

If the sacrifice is injured by the Sâma-veda side, let him offer a libation in the Âhavanîya fire, saying, Svah, Svâhâ! Thus does he bind together and heal, by means of the essence and the power of the Sâman verses themselves, whatever break the Sâman sacrifice may have suffered.

As one binds (softens) gold by means of lavana (borax), and silver by means of gold, and tin by means of silver, and lead by means of tin, and iron (loha) by means of lead, and wood by means of iron, or also by means of leather,

Thus does one bind together and heal any break in the sacrifice by means of (the Vyâhritis or sacrificial interjections which are) the essence and strength of the three worlds, of the deities, and of the threefold knowledge. That sacrifice is healed in which there is a Brahman priest who knows this.

That sacrifice is inclined towards the north (in the right way) in which there is a Brahman priest who knows this. And with regard to such a Brahman priest there is the following Gâthâ: 'Wherever it falls back, thither the man goes,'— viz. the Brahman only, as one of the Ritvig priests. 'He saves the Kurus as a mare' (viz. a Brahman priest who knows this, saves the sacrifice, the sacrificer, and all the other priests). Therefore let a man make him who knows this his Brahman priest, not one who does not know it, who does not know it.