Deuteronomy 21:2-4

Amplified Bible

² then your elders and judges shall go out and measure the distance to the cities which are around the dead person. ³ It shall be that the elders of the city which is nearest to the dead man shall take a heifer of the herd, one which has not been worked and which has not pulled in a yoke; ⁴ and the elders of that city shall bring the heifer down to a [river] valley with running water, which has not been plowed or planted, and shall break the heifer’s neck there in the valley.