Judges 20:29-31

20:29 So Israel hid men in ambush outside Gibeah. 20:30 The Israelites attacked the Benjaminites the next day; they took their positions against Gibeah just as they had done before. 20:31 The Benjaminites attacked the army, leaving the city unguarded. They began to strike down their enemy just as they had done before. On the main roads (one leads to Bethel, the other to Gibeah) and in the field, they struck down about thirty Israelites.