The Holy Bible, Revelation 14:1-5
1 And I looked, and, lo, a Lamb stood on the mount Sion, and with him an hundred forty and four thousand, having his Father’s name written in their foreheads.
2 And I heard a voice from heaven, as the voice of many waters, and as the voice of a great thunder: and I heard the voice of harpers harping with their harps:
3 And they sung as it were a new song before the throne, and before the four beasts, and the elders: and no man could learn that song but the hundred and forty and four thousand, which were redeemed from the earth.
4 These are they which were not defiled with women; for they are virgins. These are they which follow the Lamb whithersoever he goeth. These were redeemed from among men, being the firstfruits unto God and to the Lamb.
5 And in their mouth was found no guile: for they are without fault before the throne of God.
The Holy Bible, Revelation 7:2-8
2 And I saw another angel ascending from the east, having the seal of the living God: and he cried with a loud voice to the four angels, to whom it was given to hurt the earth and the sea,
3 Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.
4 And I heard the number of them which were sealed: and there were sealed an hundred and forty and four thousand of all the tribes of the children of Israel.
5 Of the tribe of Juda were sealed twelve thousand. Of the tribe of Reuben were sealed twelve thousand. Of the tribe of Gad were sealed twelve thousand.
6 Of the tribe of Aser were sealed twelve thousand. Of the tribe of Nepthalim were sealed twelve thousand. Of the tribe of Manasses were sealed twelve thousand.
7 Of the tribe of Simeon were sealed twelve thousand. Of the tribe of Levi were sealed twelve thousand. Of the tribe of Issachar were sealed twelve thousand.
8 Of the tribe of Zabulon were sealed twelve thousand. Of the tribe of Joseph were sealed twelve thousand. Of the tribe of Benjamin were sealed twelve thousand.
The Doctrine and Covenants, Section 133:18
18 When the Lamb shall stand upon Mount Zion, and with him a hundred and forty-four thousand, having his Father’s name written on their foreheads.
The Doctrine and Covenants, Section 77:11
11 Q. What are we to understand by sealing the one hundred and forty-four thousand, out of all the tribes of Israel–twelve thousand out of every tribe? A. We are to understand that those who are sealed are high priests, ordained unto the holy order of God, to administer the everlasting gospel; for they are they who are ordained out of every nation, kindred, tongue, and people, by the angels to whom is given power over the nations of the earth, to bring as many as will come to the church of the Firstborn.
The Doctrine and Covenants, Section 77:9
9 Q. What are we to understand by the angel ascending from the east, Revelation 7th chapter and 2nd verse? A. We are to understand that the angel ascending from the east is he to whom is given the seal of the living God over the twelve tribes of Israel; wherefore, he crieth unto the four angels having the everlasting gospel, saying: Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads. And, if you will receive it, this is Elias which was to come to gather together the tribes of Israel and restore all things.
History of the Church, Joseph Smith 5:326
At the close of the meeting…I remarked that the hundred and forty-four thousand sealed are the priests who should be anointed to administer in the daily sacrifice.
History of the Church, Joseph Smith 6:196
I attended prayer-meeting with the quorum in the assembly room, and made some remarks respecting the hundred and forty-four thousand mentioned by John the Revelator, showing that the selection of persons to form that number had already commenced.
Journal of Discourses, Orson Pratt 15:45
When the Temple is built the sons of the two Priesthoods…will enter into that Temple in this generation…and all of them who are pure in heart will behold the face of the Lord and that too before he comes in his glory in the clouds of heaven, for he will suddenly come to his Temple, and he will purify the sons of Moses and of Aaron, until they shall be prepared to offer in that Temple an offering that shall be acceptable in the sight of the Lord. In doing this, he will purify not only the minds of the Priesthood in that Temple, but he will purify their bodies until they shall be quickened, renewed and strengthened, and they will be partially changed, not to immortality, but changed in part that they can be filled with the power of God, and they can stand in the presence of Jesus, and behold his face in the midst of that Temple. This will prepare them for further ministrations among the nations of the earth, it will prepare them to go forth in the days of tribulation and vengeance upon the nations of the wicked, when God will smite them with pestilence, plague and earthquake, such as former generations never knew. Then the servants of God will need to be armed with the power of God, they will need to have that sealing blessing pronounced upon their foreheads that they can stand forth in the midst of these desolations and plagues and not be overcome by them. When John the Revelator describes this scene he says he saw four angels sent forth, ready to hold the four winds that should blow from the four quarters of heaven. Another angel ascended from the east and cried to the four angels, and said, “Smite not the earth now, but wait a little while.” “How long?” “Until the servants of our God are sealed in their foreheads.” What for? To prepare them to stand forth in the midst of these desolations and plagues, and not be overcome. When they are prepared, when they have received a renewal of their bodies in the Lord’s Temple, and have been filled with the Holy Ghost and purified as gold and silver in a furnace of fire, then they will be prepared to stand before the nations of the earth and preach glad tidings of salvation in the midst of judgments that are to come like a whirlwind upon the wicked.
Journal of Discourses, Orson Pratt Pratt 18:4
How long will they who come from the north countries tarry in the heights of Zion? Some time. They have got to raise wheat, cultivate the grape, wine and oil, raise flocks and herds, and their souls will have to become as a watered garden. They will dwell in Zion a good while, and during that time, there will be twelve thousand chosen out of each of these ten tribes, besides twelve thousand that will be chosen from Judah, Joseph, and the remaining tribes, one hundred and forty-four thousand in all. Chosen for what? To be sealed in their foreheads. For what purpose? So that the power of death and pestilence and plague that will go forth in those days sweeping over the nations of the earth will have no power over them. These parties who are sealed in their foreheads will go forth among all people, nations and tongues, and gather up and hunt out the house of Israel, wherever they are scattered, and bring as many as they possibly can into the Church of the firstborn, preparatory to the great day of the coming of the Lord. One hundred and forty-four thousand missionaries! Quite a host. All this has got to take place. There are persons in this congregation who will be in the midst of Zion, when the ten tribes come to Zion from the north countries, and will assist in bestowing the blessings promised by the Almighty upon the heads of the tribes of Israel. There are servants of God in the midst of this congregation who will lay their hands upon many of each of these twelve thousand, chosen out of the ten tribes, and set them apart as missionaries to visit the nations of the earth and hunt up the remnants of the seed of Jacob.
Journal of Discourses, Orson Pratt Pratt 18:7
And when they come to the height of Zion they shall be crowned with glory under the hands of the servants of God living in those days, the children of Ephraim, crowned with certain blessings that pertain to the Priesthood, that they could not receive in their own lands. In that day will be set apart twelve thousand out of each of these ten tribes–one hundred and twenty thousand persons ordained to the High Priesthood, after the order of the Son of God, to go forth to all people, nations, kindreds and tongues, for the salvation of the remnants of Israel in the four quarters of the earth, to bring as many as will come unto the Church of the Firstborn. Thus God will have twelve thousand out of all the tribes of Israel to fulfill his purposes; and when they have completed his work here on the earth, they will be called home to Zion, be crowned with glory and stand upon Mount Zion and sing the song of the redeemed, the song of the hundred and forty-four thousand, and the Father’s name will be written in their foreheads.