Revelation 6:9-11

When the Lamb broke open the fifth seal, I saw at the foot of the altar the souls of those whose lives had been sacrificed for [adhering to] the Word of God and for the testimony they had borne. They cried in a loud voice, O [Sovereign] Lord, holy and true, how long now before You will sit in judgment and avenge our blood upon those who dwell on the earth? [Gen. 4:10; Ps. 79:5; Zech. 1:12.] Then they were each given a long and flowing and festive white robe and told to rest and wait patiently a little while longer, until the number should be complete of their fellow servants and their brethren who were to be killed as they themselves had been.