Where did the sages of blessed memory get this idea recorded in the Babylonian Talmud Rosh Hashana 31b of tying a red or crimson cord to the goat sent to azazel (last week's Torah reading), in order to see if this red crimson cord would turn white?
I have read other questions in regards to this goat here at Mi Yodeya, but not this particular question.
Did the rabbis ever talk about where the sages got this idea of tying a red cord on the goat, perhaps for example, from Isaiah 1:18? "Come now, let us debate, says the Lord. If your sins prove to be like crimson, they will become white as snow; if they prove to be as red as crimson dye, they shall become as wool." (I saw this verse from a Chabad Website, but it was not connected to the goat sent to Azazel.)