Doctrine & Covenants 110:14-16

“Behold, the time has fully come, which was spoken of by the mouth of Malachi---testifying that he [Elijah] should be sent, before the great and dreadful day of the Lord come---To turn the hearts of the fathers to the children, and the children to the fathers, lest the whole earth be smitten with a curse---Therefore, the keys of this dispensation are committed into your hands; and by this ye may know that the great and dreadful day of the Lord is near, even at the doors.”