Revelation 7:13-14

13Then one of the leaders asked me, ‘Who are these people in white clothes? Where did they come from?’

14I replied, ‘You surely know who they are, sir.’ He said to me, ‘They are the people who have had a time of very bad trouble. Now they have come out of that. They have washed their clothes in the blood of the Lamb. Now their clothes are white and clean.