וַיִּנָּֽחֲמוּ֙ בְּנֵ֣י יִשְׂרָאֵ֔ל אֶל־בִּנְיָמִ֖ן אָחִ֑יו וַיֹּ֣אמְר֔וּ נִגְדַּ֥ע הַיּ֛וֹם שֵׁ֥בֶט אֶחָ֖ד מִיִּשְׂרָאֵֽל׃
And the children of Israel repented them for Benjamin their brother, and said: ‘There is one tribe cut off from Israel this day.
Read midrashic interpretation of Judges 21:6: and classical rabbinic exegesis.