Revelation 6:10-11

and they cried with a great voice, saying, How long, O Master, the holy and true, dost thou not judge and avenge our blood on them that dwell on the earth? And there was given them to each one a white robe; and it was said unto them, that they should rest yet for a little time, until their fellow-servants also and their brethren, which should be killed even as they were, should be fulfilled.