Revelation 6:9-11

When he opened the fifth seal, I saw under the altar the souls of those who had been slaughtered because of the word of God and the testimony they had given. They cried out with a loud voice, “Lord, the one who is holy and true, how long until you judge those who live on the earth and avenge our blood?” So they were each given a white robe, and they were told to rest a little while longer until the number would be completed of their fellow servants and their brothers and sisters, who were going to be killed just as they had been.