The word(s) "dumb" appears 6 time(s) in 6 verse(s) in Quran in Mohsin Khan translation.

(1) They are deaf, dumb, and blind, so they return not (to the Right Path).

(2) And the example of those who disbelieve is as that of him who shouts to those (flock of sheep) that hears nothing but calls and cries. (They are) deaf, dumb and blind. So they do not understand. (Tafsir Al-Qurtubi )

(3) Those who reject Our Ayat (proofs, evidence, verses, lessons, signs, revelations, etc.) are deaf and dumb in the darkness. Allah sends astray whom He wills and He guides on the Straight Path whom He wills.

(4) Verily! The worst of (moving) living creatures with Allah are the deaf and the dumb, who understand not (i.e. the disbelievers).

(5) And Allah puts forward (another) example of two men, one of them dumb, who has no power over anything (disbeliever), and he is a burden on his master; whichever way he directs him, he brings no good. Is such a man equal to one (believer in the Islamic Monotheism) who commands justice, and is himself on the Straight Path?

(6) And he whom Allah guides, he is led aright; but he whom He sends astray, for such you will find no Auliya' (helpers and protectors), besides Him, and We shall gather them together on the Day of Resurrection on their faces, blind, dumb and deaf; their abode will be Hell; whenever it abates, We shall increase for them the fierceness of the Fire.