This is what the verse said: “You sit and speak against your brother; you slander your mother’s son [ben imekha]” (Psalms 50:20). Rabbi Yoḥanan said: If you accustomed your tongue to speak against your brother14Meaning, your friend. who is not a member of your nation [ben umatekha], ultimately you will slander a member of your nation. Rabbi Yehuda ben Levi said: If you accustomed your tongue to speak against your paternal brother who is not your maternal brother, ultimately you will slander your maternal brother.
For anyone who is so arrogant as to speak against someone greater than he, [he] brings it about that leprosy comes upon him. If you do not believe it, let the righteous Miriam15Who spoke against Moses. be a model for all who engage in malicious speech. That is, “Remember what the Lord your God did to Miriam.”