משנה אויף ויקרא 15:17

How do we know that if one [a woman] discharges semen on the third day she is unclean? Because it is said, “Be ready for the third day” (Exodus 19:15). How do we know that one who has been circumcised may be bathed on the third day [after circumcision] which falls on Shabbat? Because it is said, “And it came to pass on the third day, when they were in pain” (Genesis 34:25). How do we know that a crimson-colored strap is tied to the head of the goat that is sent [to Azazel]? Because it is said, “If your sins be as scarlet, they shall be as white as snow” (Isaiah 1:18).