Old Testament readings use the Septuagint , the Scripture the apostles quoted. Masoretic numbering shown for reference.Learn why
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Judges 20:31

The children of Benjamin went out against the people, and were drawn away from the city; and they began to strike and kill of the people as at other times, in the highways, of which one goes up to Bethel and the other to Gibeah, in the field, about thirty men of Israel.

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