Isaiah 28:11 But he will speak to this nation with stammering lips and in another language; (WEB KJV JPS DBY WBS NAS)
Isaiah 32:4 The heart also of the rash shall understand knowledge, and the tongue of the stammerers shall be ready to speak plainly. (See NIV)
Isaiah 33:19 Thou shalt not see a fierce people, a people of a deeper speech than thou canst perceive; of a stammering tongue, that thou canst not understand. (KJV JPS DBY WBS NAS RSV)