Leviticus 14:4-6

the priest shall order that two live clean birds and some cedar wood, scarlet yarn and hyssop be brought for the person to be cleansed. Then the priest shall order that one of the birds be killed over fresh water in a clay pot. He is then to take the live bird and dip it, together with the cedar wood, the scarlet yarn and the hyssop, into the blood of the bird that was killed over the fresh water.