וְעַתָּה֙ אַל־תְּנַקֵּ֔הוּ כִּ֛י אִ֥ישׁ חָכָ֖ם אָ֑תָּה וְיָֽדַעְתָּ֙ אֵ֣ת אֲשֶׁ֣ר תַּֽעֲשֶׂה־לּ֔וֹ וְהוֹרַדְתָּ֧ אֶת־שֵׂיבָת֛וֹ בְּדָ֖ם שְׁאֽוֹל׃
Und nun, lass ihn doch nicht straflos ausgehen, denn du bist ein weiser Mann und du wirst wissen, was du ihm tun sollst, dass du sein greises Haupt senkest mit Blut in die Gruft.
Rashi
For you are a wise man. Turn your attention to find for him a capital iniquity on account of another matter. This is [what it means by], “You will know how to deal with him.”
Tze'enah Ure'enah
“And now do not let him go unpunished, etc.” [2:9]. Even though I swore to him, nonetheless he is deserving of the death penalty. You should not kill him because of my oath, but you should find an accusation against him and do not let him go free. You are wise. You will be able to find an accusation against him and cause his blood to descend to the grave.