Revelation 7:9-14 NKJV
After these things I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the throne and before the Lamb, clothed with white robes, with palm branches in their hands, and crying out with a loud voice, saying, “Salvation belongs to our God who sits on the throne, and to the Lamb!” All the angels stood around the throne and the elders and the four living creatures, and fell on their faces before the throne and worshiped God, saying:
“Amen! Blessing and glory and wisdom,
Thanksgiving and honor and power and might,
Be to our God forever and ever.
Then one of the elders answered, saying to me, “Who are these arrayed in white robes, and where did they come from?”
And I said to him, “Sir, you know.”
So he said to me, “These are the ones who come out of the great tribulation, and washed their robes and made them white in the blood of the Lamb.
NKJV: New King James Version