Revelation 6:7-11 ESV
When he opened the fourth seal, I heard the voice of the fourth living creature say, “Come!” And I looked, and behold, a pale horse! And its rider’s name was Death, and Hades followed him. And they were given authority over a fourth of the earth, to kill with sword and with famine and with pestilence and by wild beasts of the earth.
When he opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the witness they had borne. They cried out with a loud voice, “O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?” Then they were each given a white robe and told to rest a little longer, until the number of their fellow servants and their brothers should be complete, who were to be killed as they themselves had been.
ESV: English Standard Version 2016