Isaiah 32:4
The heart also of the rash shall understand knowledge, and the tongue of the stammerers shall be ready to speak plainly.

Mark 7:32-37
And they bring unto him one that was deaf, and had an impediment in his speech; and they beseech him to put his hand upon him. [33] And he took him aside from the multitude, and put his fingers into his ears, and he spit, and touched his tongue; [34] And looking up to heaven, he sighed, and saith unto him, Ephphatha, that is, Be opened. [35] And straightway his ears were opened, and the string of his tongue was loosed, and he spoke plain. [36] And he charged them that they should tell no man: but the more he charged them, so much the more a great deal they published it; [37] And were beyond measure astonished, saying, He hath done all things well: he makes both the deaf to hear, and the dumb to speak.