Deuteronomy 21:2-4

2your elders and judges must go out and measure how far it is to the cities in the vicinity of the corpse.

3Then the elders of the city nearest to the corpse must take from the herd a heifer that has not been worked – that has never pulled with the yoke –

4and bring the heifer down to a wadi with flowing water, to a valley that is neither plowed nor sown. There at the wadi they are to break the heifer’s neck.