Rabbi Yehoshua of Sikhnin said in the name of Rabbi Levi: There are four matters that the evil inclination decries, as “statute” is written in their regard: A brother’s wife, mixed species, the scapegoat, and the red heifer. A brother’s wife, as it is written: “The nakedness of your brother’s wife [you shall not uncover]” (Leviticus 18:16), but without children: “Her brother-in-law shall consort with her” (Deuteronomy 25:5).
And it is written regarding the nakedness of a brother’s wife: “You shall observe all My statutes” (Leviticus 20:22).38The verse refers to all of the forbidden relations mentioned in the chapter, including a brother’s wife. Mixed species: “You shall not wear a mixture of fibers [wool and linen together]” (Deuteronomy 22:11), but a linen cloak with woolen fringes is permitted. And it is written in its regard: “You shall observe My statutes…[and clothing of mixed fiber shall not be placed on you]” (Leviticus 19:19).
The scapegoat, as it is written: “And the one who dispatches the goat to Azazel shall wash his garments” (Leviticus 16:26), but it itself [the scapegoat] atones for others. And it is written in its regard: “This shall be for you an eternal statute” (Leviticus 16:34). The heifer, from where is it derived? It is as we learn: Those dealing with the heifer, from beginning to end, impurify their garments,39Mishna Para 4:4. but it itself purifies garments. And a statute is written in its regard: “This is the statute of the Torah.”