Translation: Korihor, the anti-Christ, travels around teaching people that there is no Christ. Alma testifies of Christ, so Korihor challenges Alma asking for a sign that God exists. The sign is that Korihor is struck dumb. The story is shared in Alma 30:6-60.
Alma 30:43 – “And now Korihor said unto Alma: If thou wilt show me a sign, that I may be convinced that there is a God, yea, show unto me that he hath power, and then will I be convinced of the truth of thy words.”