Śaṅkaraon Brahma Sūtra 2.4.18

The pr&wa is everywhere spoken of as different from speech, &c. The passage, e.g. beginning with ‘ They said to speech ’ (Bri. Up. I, 3, 2), enumerates speech, &c., which were overwhelmed by the evil of the Asuras, concludes thereupon the section treating of speech, &c., and then specially mentions the mukhya pra;/a as overcoming the Asuras, in the paragraph beginning ‘ Then they said to the breath in the mouth.’—Other passages also referring to that difference may be quoted, so, for instance, ‘ He made mind, speech, and breath for himself’ (Bri. Up. I, 5, 3).—For this reason also the other pranas are different in being from the chief pra/^a. Another reason follows.