וַיֹּאמְר֑וּ הַכְזוֹנָ֕ה יַעֲשֶׂ֖ה אֶת־אֲחוֹתֵֽנוּ׃
And they said: Should he deal with our sister as with a harlot?
Torah Temimah points to Bereshit Rabbah 80:12.
Sefaria · Bereshit Rabbah 80:12
הכזונה יעשה את אחותנו — כזונה אין עושין.
“Should he deal with our sister as with a harlot?” — one does not treat [a sister] as a harlot.
The brothers justify their action by the principle that a sister must not be treated as a harlot.
Derash on the brothers’ reply (Bereshit Rabbah).
Shimon and Levi defend their deed by asserting that their sister must not be treated as a harlot.