The Upanishads, Part 1 (SBE01), by Max Müller, , at sacred-texts.com
1. And here they ask: 'What is the beginning of this day?' Let him say: 'Mind and speech 2.'
2. All desires dwell in the one (mind), the other yields all desires.
3. All desires dwell in the mind, for with the mind he conceives all desires.
4. All desires come to him who knows this.
5. Speech yields all desires, for with speech he declares all his desires.
6. Speech yields all desires to him who knows this.
7. Here they say: 'Let him not begin this day with a Rik, a Yagus, or a Sâman verse (divine speech), for it is said, he should not start with a Rik, a Yagus, or a Sâman 3.'
8. Therefore, let him say these Vyâhritis (sacred interjections) first.
9. These interjections Bhûs, Bhuvas, Svar are the three Vedas, Bhûs the Rig-veda, Bhuvas the Yagur-veda, Svar the Sâma-veda. Therefore (by
intercalating these) he does not begin simply with a Rik, Yagus, or Sâman verse, he does not start with a Rik, Yagus, or Sâman verse.
177:2 Mind, to think about the hymns which have to be recited; speech, to recite them without a flaw.
177:3 It is doubtful whether neyâd rikah and apagakkhet can have this meaning. However, what is intended is clear, viz. that the priest, even after having uttered the sound Him, should not immediately begin with verses from the Vedas, but should intercalate the three syllables bhûr bhuvah svar, or, if taken singly, bhûs, bhuvas, svar.