Albert Barnes Commentary Judges 20:26

"Then all the children of Israel, and all the people, went up, and came unto Beth-el, and wept, and sat there before Jehovah, and fasted that day until even; and they offered burnt-offerings and peace-offerings before Jehovah." — Judges 20:26 (ASV)

Fasted until even - The regular time for ending a fast among the Hebrews was sunset (compare 1 Samuel 14:24; 2 Samuel 1:12). Such national fasts are called by the rabbis “fasts of the congregation,” and were prescribed in times of great affliction.

On the offerings, see Leviticus 1:3.