Mosiah - 26
Discussion related to this chapter in the Book of Mormon
Many members of the Church are led into sin by unbelievers. Alma is promised eternal life. Those who repent and are baptized gain forgiveness. Church members in sin who repent and confess to Alma and to the Lord shall be forgiven; otherwise they shall be excommunicated. Probably between 120 and 100 B.C.
Source: LDS Scriptures