וַֽיְהִי֙ מִֽמָּחֳרָ֔ת וַיַּשְׁכִּ֣ימוּ הָעָ֔ם וַיִּבְנוּ־שָׁ֖ם מִזְבֵּ֑חַ וַיַּעֲל֥וּ עֹל֖וֹת וּשְׁלָמִֽים׃ (פ)
And it came to pass on the morrow that the people rose early, and built there an altar, and offered burnt-offerings and peace-offerings.
Read midrashic interpretation of Judges 21:4: and classical rabbinic exegesis.