הלכה על סוטה 32:20

From the laws of the commandment is that which they, may their memory be blessed, said (Mishnah Negaim 14:1), "How does one purify the metsora? He would bring a new earthenware pitcher and place within it a reviit of living water," with which it would be fitting to consecrate the sprinkling water - and that measure is [rabbinic] (Sotah 16b) - "and he would bring two wild birds" that are pure, for the sake of the purification of the metsora; as it is stated (Leviticus 14:4), "and it shall be taken for the one being purified." He slaughters the clarified (meaning, choice) of the two of them upon the water in the earthenware vessel and squeezes until the blood is recognizable in the water. And he digs and buries the slaughtered bird before him - and this is a tradition from what was heard. He takes cedar wood - and its commandment is that it be an ell long and its width be like a quarter of a foot of the feet of a bed; and not less than a handbreadth of hyssop that does not have an adjunct name; wool dyed red, the weight of which is a shekel, and if he mixed [its color], he disqualified it, like the dying of the aquamarine, which is disqualified by mixing. And all the measures are a law [from Moshe at Sinai] (Eruvin 4a). And he takes the living bird with the three of them; and the four species impede one another (Menachot 27a); and cedar wood or hyssop that have been peeled are disqualified. He ties the hyssop to the cedar wood with a strip of crimson fabric and surrounds them with the tips of the wings and the tip of the tail of the living bird. And he dips the four of them in water that is in the vessel and in the blood that is [in] it; "and sprinkles seven times on the back of the hand of the metsora." And he sends away the bird. And how does he send it away? If he is standing in the city, he throws it out of the wall (Kiddushin 57b). "He does not face the sea nor the city, but the desert, as it is stated (Leviticus 14:53), 'to outside the city toward the field'"(Mishnah Negaim 14:2). [If] he sent it and it comes back, he again sends it away - even a hundred times.