Samuel the Lamanite prophesied that on the American continents at the time of the resurrection of Jesus Christ "many graves shall be opened, and shall yield up many of their dead; and many saints shall appear unto many." (Helaman 14:25.) This prophecy is not only literally fulfilled later in the Book of Mormon, but also, during his appearance to the righteous Nephites, the resurrected Jesus Christ instructed that an account of the fulfillment of this prophecy should be written in their records. In fact, the Savior says he commanded Samuel the Lamanite to prophesy concerning this event. (See 3 Nephi 23:9-13.)
A similar event of graves being opened also occurred on the eastern continent at the time of the resurrection of the Savior: "And the graves were opened; and many bodies of the saints which slept arose, and came out of the graves after his resurrection, and went into the holy city, and appeared unto many." (Matthew 27:52-53.)