Chandogya Upanishad 7.5.1

7.5.1

cittaṃ vāva saṃkalpād bhūyaḥ \
yadā vai cetayate atha saṃkalpayate \
atha manasyati \
atha vācam īrayati \
tām u nāmnīyūati \
nāmni mantrā ekaṃ bhavanti \
mantreṣu karmāṇi \\705.1\

1. ‘Thought (_citta_), assuredly, is more than Conception. Verily, when one thinks, then he forms a conception, then he has in Mind, then he utters Speech, and he utters it in Name. The sacred sayings (_mantra_) are included in Name; and sacred works in the sacred sayings.