Revelation 6:9-11 - The Fifth Seal
9 And when the Lamb broke open the fifth seal, I saw underneath the altar the souls of those who had been killed for [believing and preaching] God's message, and for the testimony [about Jesus] which they had maintained. 10 And they called out with a loud voice, "How long, holy and true Master, [will it be] before you judge the people living on earth and take revenge on them for [shedding] our blood?" 11 And a white robe was given to each one of them, and they were told to rest a little while longer, until the [full] number of their fellow servants and their brothers would be killed like they were.