Revelation 7:13-14 (ESV)

Then one of the elders addressed me, saying, “Who are these, clothed in white robes, and from where have they come?”

“These are the ones coming out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb.”

The Four and Twenty Elders
Henry John Stock (English, 1853-1930)