Revelation 6:9

6:9 Now when the Lamb opened the fifth seal, I saw under the altar the souls of those who had been violently killed because of the word of God and because of the testimony they had given.

Revelation 7:2

7:2 Then I saw another angel ascending from the east, who had the seal of the living God. He shouted out with a loud voice to the four angels who had been given permission to damage the earth and the sea: