Prophets witness of Christ

The prophets of old testified of the coming of the Son of God.

Alma in witnessing of Christ's coming, told about three others: Moses,
Zenos and Zenock.

In the wilderness Moses raised the symbol of Christ which was a
serpent of brass. Those who looked at the symbol were healed and
those who didn't died (verses 19-20).

Zenos bore testimony of the atonement of the Savior in his own life
when he said, "Thou hast turned away thy judgments because of thy Son"
(verse 13).

And Zenock spoke of the mercies of God bestowed upon his children
because of Jesus Christ (verse 16).

Finally, Alma bore his own witness in verse 22: "If so, wo shall come
upon you; but if not so, then cast about your eyes and begin to
believe in the Son of God, that he will come to redeem his people, and
that he shall suffer and die to atone for their sins; and that he
shall rise again from the dead, which shall bring to pass the
resurrection, that all men shall stand before him, to be judged at the
last and judgment day, according to their works."

Source: Alma 33 in the Book of Mormon (http://scriptures.lds.org/en/alma/33)