Sabbath, April 3rd He [Joseph Smith] attended meeting in the Lord's House [Kirtland Temple]... he retired to the pulpit, the vails being dropped, and bowed himself, with O[liver] Cowdery, in solemn but silent prayer to the Most High.
After rising from prayer the following vision was opened to both of them. The vail was taken from their minds and the eyes of their understandings were opened. They saw the Lord standing upon the breast work of the pulpit before them and under his feet was a paved work of pure gold, in color like amber. His eyes were as a flame of fire; the hair of his head was like the pure snow. His countenance shone above the brightness of the sun, and his voice was as the sound of the rushing of great waters, even the Voice of Jehovah, saying, "I am the first and the last. I am he who liveth. I am he who was slain. I am your Advocate with the Father. Behold your sins are forgiven you. You are clean before me. Therefore lift up your heads and rejoice. Let the hearts of all my brethren /people/ rejoice, who have, with their might, built this house to my name.
"For behold I have accepted this house and my name shall be here; and I will manifest myself to my people, in mercy, in this House. Yea, I will appear unto my servants and speak unto them with mine own voice, if my people will keep my commandments and do not pollute this Holy House. Yea, the hearts of thousands and tens of thousands shall greatly rejoice in consequence of the blessings which shall be poured out and the endowment with which my servants have already been endowed and shall hereafter be endowed in this House. And the fame of this House shall spread to foreign lands, and this is the beginning of the blessing, which shall be poured out upon the heads of my people. Even so. Amen."
After this vision closed, the Heavens were again opened unto them and Moses appeared before them and committed unto them the keys of the gathering of Israel from the four parts of the Earth and the leading of the ten tribes from the Land of the North. After this Elias appeared and committed the dispensation of the gospel of Abraham, saying, that in them and their seed all generations after them should be blessed.
After this vision had closed, another great and glorious vision burst upon them, for Elijah the Prophet, who was taken to Heaven without tasting death, also stood before them, and said, "Behold the time has fully come which was spoken of by the mouth of Malachi, testifying, that he 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 the dreadful day of the Lord is near, even at the doors." [See D&C 110]
[Faulring, Scott (ed.), An American Prophet's Record: The Diaries and Journals of Joseph Smith: Joseph Smith Diary, 1835-36, http://amzn.to/jsdiaries]