Alma 18:34 through 41, 19 6 and 33.
Ammon said unto him: I am a man; and man in the beginning was created after the image of God, and I am called by his Holy Spirit to teach these things unto this people, that they may be brought to a knowledge of that which is just and true;
And a portion of that Spirit dwelleth in me, which giveth me knowledge, and also power according to my faith and desires which are in God.
Now when Ammon had said these words, he began at the creation of the world, and also the creation of Adam, and told him all the things concerning the fall of man, and rehearsed and laid before him the records and the holy scriptures of the people, which had been spoken by the prophets, even down to the time that their father, Lehi, left Jerusalem.
And he also rehearsed unto them (for it was unto the king and to his servants) all the journeyings of their fathers in the wilderness, and all their sufferings with hunger and thirst, and their travail, and so forth.
And he also rehearsed unto them concerning the rebellions of Laman and Lemuel, and the sons of Ishmael, yea, all their rebellions did he relate unto them; and he expounded unto them all the records and scriptures from the time that Lehi left Jerusalem down to the present time.
But this is not all; for he expounded unto them the plan of redemption, which was prepared from the foundation of the world; and he also made known unto them concerning the coming of Christ, and all the works of the Lord did he make known unto them.
And it came to pass that after he had said all these things, and expounded them to the king, that the king believed all his words.
And he began to cry unto the Lord, saying: O Lord, have mercy; according to thy abundant mercy which thou hast had upon the people of Nephi, have upon me, and my people. 
Now, this was what Ammon desired, for he knew that king Lamoni was under the power of God; he knew that the dark veil of unbelief was being cast away from his mind, and the light which did light up his mind, which was the light of the glory of God, which was a marvelous light of his goodness--yea, this light had infused such joy into his soul, the cloud of darkness having been dispelled, and that the light of everlasting life was lit up in his soul, yea, he knew that this had overcome his natural frame, and he was carried away in God--
And it came to pass that when Ammon arose he also administered unto them, and also did all the servants of Lamoni; and they did all declare unto the people the selfsame thing--that their hearts had been changed; that they had no more desire to do evil.