Revelation 6:9-11

When he opened the fifth seal, I saw underneath the altar the souls of those who had been killed for the Word of God, and for the testimony of the Lamb which they had. They cried with a loud voice, saying, “How long, Master, the holy and true, until you judge and avenge our blood on those who dwell on the earth?” A long white robe was given to each of them. They were told that they should rest yet for a while, until their fellow servants and their brothers, who would also be killed even as they were, should complete their course.