Revelation 6:9-11

When the Lamb broke the fifth seal, I saw underneath the altar the souls of those who had been slain because of the word of God, and because of the testimony which they had maintained; and they cried out with a loud voice, saying, “How long, O Lord, holy and true, will You refrain from judging and avenging our blood on those who dwell on the earth?” And there was given to each of them a white robe; and they were told that they should rest for a little while longer, until the number of their fellow servants and their brethren who were to be killed even as they had been, would be completed also.