Matthew 9:32-33:

As they went out, behold, they brought to him a dumb man possessed with a devil.
And when the devil was cast out, the dumb spake: and the multitudes marvelled, saying, It was never so seen in Israel.

Notes on Matthew 9:32-33:

The word “dumb” in the King James means “non-speaking,” not “stupid” as in the modern usage of the word (for example, “Books written against divine healing are full of dumb arguments”).

There are cases where a demon impels someone to never say anything.  I ministered to such a man in a nursing home for the mentally ill, and he spoke for the first time in a long while.  There was nothing physically wrong with his vocal cords; it was a demonic issue.  We have authority to cast out “mute spirits” today when we encounter them.  If there were mute spirits then, there are mute spirits today, since they’ve never left the earth.  They just look for new victims to oppress when the old victim dies or gets delivered.

See also:

Luke 11:14
Condition: Demon Possession
Condition: Dumbness