Revelation 6:9

9 Then the Lamb broke open the fifth seal. I saw underneath the altar the souls of those who had been killed because they had proclaimed God's word and had been faithful in their witnessing.

Revelation 6:9 In-Context

7 Then the Lamb broke open the fourth seal; and I heard the fourth living creature say, "Come!"
8 I looked, and there was a pale-colored horse. Its rider was named Death, and Hades followed close behind. They were given authority over one fourth of the earth, to kill by means of war, famine, disease, and wild animals.
9 Then the Lamb broke open the fifth seal. I saw underneath the altar the souls of those who had been killed because they had proclaimed God's word and had been faithful in their witnessing.
10 They shouted in a loud voice, "Almighty Lord, holy and true! How long will it be until you judge the people on earth and punish them for killing us?"
11 Each of them was given a white robe, and they were told to rest a little while longer, until the complete number of other servants and believers were killed, as they had been.
Scripture taken from the Good News Translation - Second Edition, Copyright 1992 by American Bible Society. Used by Permission.