The power of God was upon Alma and so he prepared to pronounce judgment on Korihor:
“Now Alma said unto him: This will I give unto thee for a sign, that thou shalt be struck dumb, according to my words; and I say, that in the name of God, ye shall be struck dumb, that ye shall no more have utterance. Now when Alma had said these words, Korihor was struck dumb, that he could not have utterance, according to the words of Alma.”