Must Be Married by the Power & Authority of the Priesthood to Have Children in the Resurrection — William Clayton (May 16, 1843)
He said that except a man and his wife enter into an everlasting covenant and be married for eternity while in this probation by the power and authority of the Holy priesthood they will cease to increase when they die (i e) they will not have any children in the resurrection, but those who are married by the power & authority of the priesthood in this life & continue without committing the sin against the Holy Ghost will continue to increase & have children in the celestial glory.
Instruction, 16 May 1843, as Reported by William Clayton, pp. 14-15, The Joseph Smith Papers.
