Doctrine and Covenants 1:37-38

37 ^aSearch these ^bcommandments, for they are true and ^cfaithful, and the prophecies and ^dpromises which are in them shall all be fulfilled.

38 What I the Lord have spoken, I have spoken, and I excuse not myself; and though the heavens and the earth pass away, my ^aword shall not pass away, but shall all be ^bfulfilled, whether by mine own ^cvoice or by the ^dvoice of my ^eservants, it is the ^fsame.