Alma 45:10

And these are the words: Behold, I perceive that this very people, the Nephites, according to the spirit of revelation which is in me, in four hundred years from the time that Jesus Christ shall manifest himself unto them, shall dwindle in unbelief;

“These are the words: I know that this very people, the Nephites, will stop believing in four hundred years from the time that Jesus Christ shows himself to them. I know this because of the Spirit that is in me.”

“Here’s what I see: Four hundred years after Jesus Christ appears to this people, the Nephites will collapse into unbelief. The Spirit shows me this.”