Mon Nazir 51

The gemara says that if someone finds three dead bodies in a field within a certain distance that we can assume that there was a cemetery there, you can't exhume them. We assume that this was a old cemetery, which they have a right to remain there, and not just temporarily buried there and forgotten about.

The Gemara says: if one of the dead was found missing some limb, we don't count it as one of the three, and you may exhume them.

Tosfos asks: what difference does it make which shape you find the dead. As long as you find three in a row is a sign that there was a cemetery. So even if one is not complete should also show that?

Tosfos answers: If we say that this Halacha does not come from logic, but rather a Halacha L'moshe M'sinai. We only consider it to be a proper cemetery because the Torah decreed so, then we can say the certain disparage in the halcha, that we don't count the dead with missing limbs, are also part of this decree.