Revelation 6:9-12

When He (the Lamb) broke open the fifth seal, I saw underneath the altar the souls of those who had been slaughtered because of the word of God, and because of the testimony which they had maintained [out of loyalty to Christ]. They cried in a loud voice, saying, “O Lord, holy and true, how long now before You will sit in judgment and avenge our blood on those [unregenerate ones] who dwell on the earth?” [Gen 4:10; Ps 79:10; 94:3; Zech 1:12] Then they were each given a white robe; and they were told to rest and wait quietly for a little while longer, until the number of their fellow servants and their brothers and sisters who were to be killed even as they had been, would be completed. I looked when He (the Lamb) broke open the sixth seal, and there was a great earthquake; and the sun became black as sackcloth [made] of hair, and the whole moon became like blood; [Joel 2:10, 31]