THE CRIMSON THREAD AT THE TEMPLE

R. Nahum b. Papa said in the name of R. Eleazar ha Kappar: Originally they used to tie the thread of crimson wool to the entrance of the Ulam within, and as soon as the he goat reached the wilderness, it turned white. Then they knew that the commandment concerning it had been fulfilled, as it is said: If your sins be as scarlet, they shall be as white wool (Yoma 67a)