Revelation 6:8-11

8Behold, I saw a horse, pale greenish gray. The name of the one riding on it was Death, and Sheol was following with him. Authority was given to them over a fourth of the earth, to kill by sword and by famine and by plague and by the wild beasts of the earth.

9When the Lamb opened the fifth seal, I saw under the altar the souls of those slaughtered for the sake of the word of God and for the witness they had.

10And they cried out with a loud voice, saying, “O Sovereign Master, holy and true, how long before You judge those who dwell on the earth and avenge our blood?”

11Then a white robe was given to each of them, and they were told to rest a little while longer, until the number of their fellow servants was complete—their brothers and sisters who were to be killed as they had been.