Therefore when he sees the boy, without a pause for thought, reading off seven or five lines at a breath, he will not easily be induced to believe that he has not read the book before; and certainly not, if he is able also to observe the appropriate enunciation, the proper separations of the words, and the correct use of the rough and smooth breathings. ― translation from: Evelyn Shirley Shuckburgh, The Histories of Polybius (1889), book X, chapter xlvii: “Importance of Practice”
This is one group of voiceless letters, all three letters being pronounced with a similar configuration ⟨of the mouth⟩, but differing in smoothness and roughness. ― translation from: Stephen Usher, opere citatoLCL 466 (1985), chapter xiv, paragraph 6, page 103, lines 13–16
ante AD 210, Sextus Empiricus (author), Jürgen Mau (editor), Πρὸς Μαθηματικούς in Sexti Empirici Opera rec. Hermannus Mutschmann, Leipzig: in aedibus B.G. Teubneri, volume III: Adversus Mathematicos libros I–VI continens (1954), book i: «Πρὸς Γραμματικούς», chapter: ‹ὅτι ἀμέθοδόν ἐστι καὶ ἀσύστατον τὸ τεχνικὸν τῆς γραμματικῆς μέρος›, § 103 (page 27, lines 7–12; Bekk. p. 622, lines 6–12):