I am grateful for G.K. Beale's large commentary on Revelation. It helped me to track down these passages as they possibly relate to the great crowd of Revelation 7:9-17.
"Binding his foal unto the vine, and his ass's colt unto the choice vine, he washed his garments in wine, and his clothes in the blood of grapes" (Genesis 49:11, 21st Century King James Version).
"And Jehovah said unto Moses, Go unto the people, and sanctify them to-day and to-morrow, and let them wash their garments" (Exod 19:10, ASV)
"And Moses went down from the mount unto the people, and sanctified the people; and they washed their garments" (Exodus 19:14, ASV).
"Then he took the Book of the Covenant and read it aloud to the people. Again they all responded, 'We will do everything the Lord has commanded. We will obey.' Then Moses took the blood from the basins and splattered it over the people, declaring, 'Look, this blood confirms the covenant the Lord has made with you in giving you these instructions'" (Exodus 24:7-8, NLT).
"Come now, and let us reason together, saith Jehovah: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool" (Isaiah 1:18, ASV).
"When the Lord has washed away the filth of the daughters of Zion and purged the bloodshed of Jerusalem from her midst, by the spirit of judgment and the spirit of burning, then the LORD will create over the whole area of Mount Zion and over her assemblies a cloud by day, even smoke, and the brightness of a flaming fire by night; for over all the glory will be a canopy. There will be a shelter to give shade from the heat by day, and refuge and protection from the storm and the rain" (Isaiah 4:4-6)
"For we are all become as one that is unclean, and all our righteousnesses are as a polluted garment: and we all do fade as a leaf; and our iniquities, like the wind, take us away" (Isaiah 64:6, ASV).
"And he was clothed with a robe dipped in blood: and his name is called The Word of God" (Revelation 19:13, KJV 2000 Bible).
See also Zechariah 3:1-5
Beale writes that the metaphor of the great crowd washing their robes in the Lamb's blood "primarily connotes the objective reality that the saints have been cleansed from their sin by their persevering faith in Christ's death for them, that faith having been refined by trials" (page 438).