Midrash su Salmi 50:20

These are the accounts of the tabernacle (Exod. 38:21). Scripture states elsewhere: Thou hast also delivered Me from the contentions of My people (II Sam. 22:44), and it is written elsewhere: Thou hast delivered me from the contentions of the people (Ps. 18:44). The contentions of the people refers to the nations of the world, and the contentions of My people alludes to Israel. David said: Master of the Universe, the Israelites are a contentious lot; do You wish them to murmur against me amongst themselves? A proof of this is that after the Tabernacle was erected, though everything was done according to numbers and weights, as it is written: The whole by number and by weight; and all the weight was written at that time (Ezra 8:34), they became contentious, as is said: And the people spoke against God, and against Moses (Num. 21:15). Hence, it says: Thou mayest deliver me from the contentions of My people (II Sam. 22:44). This verse alludes to Moses. At the time he erected the Tabernacle, Moses said: I know that the Israelites are a troublesome lot. They speak against their brothers and their mothers, as it is said: Thou sittest and speakest against thy brother; thou slanderest thine own mother’s sons (Ps. 50:20). What is meant by Thou sittest and speakest against thy brother? R. Johanan said: You must not believe that one is permitted to speak against a brother born of one’s father, but not against a brother born of one’s mother, for if you should speak against your brother born of your father, you will eventually speak against your brother born of your mother, as it is said: Thou sittest and speakest against thine own brother; thou slanderest thine own mother’s sons.

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.

Rabbi Ishmael said: Every son of the old age || is beloved of his father, as it is said, "Now Israel loved Joseph more than all his children, because he was the son of his old age" (Gen. 37:3). Was he then the son of his old age? Was not Benjamin the son of his old age? But owing to the fact that (Jacob) saw by his prophetic power that (Joseph) would rule in the future, therefore he loved him more than all his sons. And they envied him with a great envy, as it is said, "And his brethren saw that their father loved him more than all his brethren; and they hated him" (ibid. 4). Further, because he saw in his dream that in the future he would rule, and he told his father, and they envied him yet more and more, as it is said, "And they hated him yet the more" (ibid. 8). Moreover, he saw the sons of his father's concubines eating the flesh of the roes and the flesh of the sheep whilst they were alive, and he brought a reproach against them before Jacob their father, so that they could not see his face any more (in peace), as it is said, "And they could not speak peaceably unto him" (ibid. 4). Jacob said to Joseph: Joseph, my son ! Verily I have (waited) many days without hearing of the welfare of thy brethren, and of the welfare of the flock, as it is said, "Go now, see whether it be well with thy brethren, and well with the flock" (ibid. 14). And the lad was wandering in the field, and the angel Gabriel met him, as it is said, "And a certain man found him, and, behold, he was wandering in the field" (ibid. 15). (The word) "man" (here in this context) is Gabriel only, as it is said, "The man Gabriel, whom I had seen in the vision" (Dan. 9:21).