Numbers 35:9

[So] all the cities which ye shall give to the Levites [shall be] forty and eight cities: them [shall ye give] with their suburbs.

And the cities which ye shall give [shall be] of the possession of the children of Israel: from [them that have] many ye shall give many; but from [them that have] few ye shall give few: every one shall give of his cities unto the Levites according to his inheritance which he inheriteth.

Speak unto the children of Israel, and say unto them, When ye be come over Jordan into the land of Canaan;

Then ye shall appoint you cities to be cities of refuge for you; that the slayer may flee thither, which killeth any person at unawares.