Numbers 35:8-12

As for the cities which you shall give them from the possession of the sons of Israel, you shall take more from the larger, and you shall take fewer from the smaller; each shall give some of his cities to the Levites in proportion to his inheritance which he possesses.”

Then the Lord spoke to Moses, saying,

“Speak to the sons of Israel and say to them, ‘When you cross the Jordan into the land of Canaan,

then you shall select for yourselves cities to be your cities of refuge, so that the one who commits manslaughter by killing a person unintentionally may flee there.

The cities shall serve you as a refuge from the avenger, so that the one who commits manslaughter does not die until he stands before the congregation for trial.