Revelation 6:11; Revelation 7:9; Revelation 7:13-14

11 And white robes were given unto every one of them; and it was said unto them, that they should rest yet for a little season, until their fellowservants also and their brethren, that should be killed as they were, should be fulfilled .
9 After this I beheld , and, lo , a great multitude, which no man could number , of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;
13 And one of the elders answered , saying unto me, What are these which are arrayed in white robes? and whence came they ? 14 And I said unto him, Sir, thou knowest . And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.