שָׁלַ֣ח לִפְנֵיהֶ֣ם אִ֑ישׁ לְ֝עֶ֗בֶד נִמְכַּ֥ר יוֹסֵֽף׃
[Mais déjà] il avait envoyé devant eux un homme: Joseph avait été vendu comme esclave.
Rashi
את דבתם רעה THEIR EVIL REPORT — Whatever he saw wrong in his brothers, the sons of Leah, he reported to his father: that they used to eat flesh cut off from a living animal, that they treated the sons of the handmaids with contempt, calling them slaves, and that they were suspected of living in an immoral manner. With three such similar matters he was therefore punished. In consequence of his having stated that they used to eat flesh cut off from a living animal Scripture states, (Genesis 37:31) “And they slew a he-goat" after they had sold him and they did not eat its flesh whilst the animal was still living. And because of the slander which he related about them that they called their brothers slaves — (Psalms 105:17) “Joseph was sold for a slave.” And because he charged them with immorality (Genesis 39:7) “his master’s wife cast her eyes upon him etc.” (Genesis Rabbah 84:7).
Radak
ויבא יוסף את דבתם רעה, he told his father that his brothers hated him, i.e. both the sons of the former servant maids with whom he was being raised, as well as the sons of Leah to whom he felt superior because he enjoyed preferential treatment by his father. As a result, the brothers sought pretexts to treat him meanly. Yaakov was angry at the brothers on behalf of Joseph, interpreting the brothers’ hatred of Joseph as jealousy due to his loving Joseph excessively. (verses 3 and 4). In Bereshit Rabbah 84,7 we are told that according to Rabbi Meir Joseph told his fathers that the brothers were suspect of violating the commandment not to eat flesh from a still living animal, whereas Rabbi Yehudah is supposed to have said that Joseph accused them of treating the sons of Bilhah and Zilpah with disdain, referring to them as “slaves.” Rabbi Shimon is reported as saying that Joseph accused the brothers of casting lustful glances at the local Canaanite girls. Rabbi Yehudah bar Seymon claims that G’d repaid Joseph for all three accusations as we derive from Proverbs 16,11 פלס ומאזני משפט לה', “Honest scales and weights are the Lord’s.” G’d said to him: “you accused your brothers of violating the law of אבר מן החי, you will be a witness that even when they were engaged in a sinful enterprise such as dipping your cloak in blood before presenting it to your father, they first slaughtered the male goat ritually, as is required when they would eat it. You accused them of calling the sons of Zilpah and Bilhah slaves, that is why you yourself were sold into slavery (Psalms 105, 17) You accused your brothers of looking lecherously at the local girls, I will cause you to be tempted by this very phenomenon.” This is why the Torah described the wife of Potiphar attempting to seduce Joseph (39,7)
Da'at Zekenim
ולא יכלו אחיו לענות אותו, “and his brothers were unable to answer him;” Rabbi Joseph Kara, explains this line as follows: the brothers on the one hand believed him when he said that his name was Joseph; however they could not believe that he was the Joseph whom they had sold into slavery, and that in the interval he had risen to such an exalted position, ruler over mighty Egypt. (Compare how Joseph is described in Psalms 105,17-18)
Rashi
he pursues statements which are futile He seeks to promulgate the halachah, but it is not in his possession. The midrash interprets it as concerning Joseph, who spread slander about his brothers. He would say to his father that they were suspected of [eating] limbs from a living animal. Therefore, they hated him, and he was called a poor man because he would spread false rumors about them and look for statements that were not true (לא המה). We read לו, “to him,” for he would pursue statements for his own benefit, and in Joseph’s matter, they were his, because his slander returned upon him. He would say that they ate limbs from a living animal, but Scripture testifies about them that even in the time of sin, they would slaughter a kid, as it is said: (Gen. 37:31) “and they slaughtered a kid.” He would say that they degraded the sons of the maidservants. Therefore, Joseph was sold as a slave. He would say that they gazed upon the women of the land. Said the Holy One, blessed be He, “By your life, I will incite a bear upon you.” Therefore, (ibid. 39:7) “his master’s wife lifted, etc.” [This appears] in Genesis Rabbah [see 84:7].