The Holy Bible, 1 Thessalonians 4:14-17

14 For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him.

15 For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.

16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:

17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.

The Doctrine and Covenants, Section 88:96-98

96 And the saints that are upon the earth, who are alive, shall be quickened and be caught up to meet him.

97 And they who have slept in their graves shall come forth, for their graves shall be opened; and they also shall be caught up to meet him in the midst of the pillar of heaven–

98 They are Christ’s, the first fruits, they who shall descend with him first, and they who are on the earth and in their graves, who are first caught up to meet him; and all this by the voice of the sounding of the trump of the angel of God.