Deuteronomy 21:2-4

2Then your elders and judges must come out and measure the distance to the towns that are around the slain one.

3Now the town nearest to the slain one—the elders of that city are to take from the herd a heifer that has not been used for work or pulled a yoke.

4Then the elders of that city are to bring the heifer down to a flowing wadi that has not been plowed or sown, and break the heifer’s neck there in the wadi.