Midrash su Genesi 36:29

Our Rabbis were taught: (Num. 15, 30) "But the person that doth aught with a high hand; this refers to Menasseh b. Hezekiah who sat and lectured on topics with the object of fault-finding," saying, "Could not Moses have found something better than (Gen. 36, 22) "And Lotan's sister was Thimna, or, (Ib.) she was a concubine of Eliphaz b. Esau," or that of (Ib. 13, 14) "And Reuben went in the days of the wheat harvest and found mandrakes in the field." A heavenly voice was then heard saying (Ps. 50, 20) "Thou sittest and speakest against thy brother, against thy own mother's sons thou utterest slander, etc." And to him also applies the words of tradition: (Is. 5, 18) Wee unto those that draw iniquity with the cords of falsehood, and as with a wagon-rope, sinfulnesses." What does a wagon-rope mean? A. Assi said: "In the beginning, the evil inclination appears as thin as the thread of a spider's web; and finally he becomes as thick as a wagon rope." Since we have already arrived at it, let us see what does And Lotan's sister was Thimna really mean. Thimna was a princess, as it is written (Gen. 36, 40) Duke Thimna, and dukedom means a kingdom without a crown. She desired to become a proselyte, but Abraham, Isaac, and Jacob did not accept her. And she went and became the concubine of Eliphaz b. Esau, saying it is better to be a servant in this nation than to be a princess of another. And her offspring was Amalek, who troubled Israel as a punishment to their parents, who ought not to have driven her away.