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 upheld.
In context
7When he opened the fourth seal, I heard the voice of the fourth living creature say, “Come!” 8I looked, and there was a pale green horse. Its rider’s name was Death, and Hades was following close behind him. They were given authority over a quarter of the earth, to kill by sword, by famine, by plague, and by the wild animals of the earth. 9When 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 upheld. 10They cried out in a loud voice, “How long, Sovereign Lord, holy and true, until you judge those who dwell on the earth and avenge our blood?” 11Then each of them was given a white robe, and they were told to rest a little longer, until the number would be complete of their fellow servants and brothers and sisters who were to be killed just as they had been.