Deuteronomy 4:41

The Narrative Concerning Cities of Refuge

4:41 Then Moses selected three cities in the Transjordan, toward the east.

Deuteronomy 14:28

14:28 At the end of every three years you must bring all the tithe of your produce, in that very year, and you must store it up in your villages.

Deuteronomy 19:7

19:7 Therefore, I am commanding you to set apart for yourselves three cities.