The Benjaminites came together out of the towns to Gibeah, to go out to battle against the Israelites.
On that day the Benjaminites mustered twenty-six thousand armed men from their towns, besides the inhabitants of Gibeah.
Of all this force, there were seven hundred picked men who were left-handed; every one could sling a stone at a hair, and not miss.
And the Israelites, apart from Benjamin, mustered four hundred thousand armed men, all of them warriors.
The Israelites proceeded to go up to Bethel, where they inquired of God, "Which of us shall go up first to battle against the Benjaminites?" And the Lord answered, "Judah shall go up first."
Then the Israelites got up in the morning, and encamped against Gibeah.
The Israelites went out to battle against Benjamin; and the Israelites drew up the battle line against them at Gibeah.
The Benjaminites came out of Gibeah, and struck down on that day twenty-two thousand of the Israelites.
The Israelites took courage, and again formed the battle line in the same place where they had formed it on the first day.
The Israelites went up and wept before the Lord until the evening; and they inquired of the Lord, "Shall we again draw near to battle against our kinsfolk the Benjaminites?" And the Lord said, "Go up against them."
References for Judges 20:23
So the Israelites advanced against the Benjaminites the second day.