Commentaire sur Les Nombres 35:13

שש ערי מקלט [AND AS TO THE CITIES WHICH YOU SHALL GIVE] SIX CITIES OF REFUGE (THERE SHALL BE FOR YOU] — This tells us that although Moses during his life-time set aside three cities on that side of the Jordan (Deuteronomy 4:41), they did not provide refuge until the three had been chosen which Joshua assigned in the land of Canaan on the west side of the Jordan (Sifrei Bamidbar 160:2; Makkot 9b).

The three that Yehoshua placed. Rashi wishes to answer the question: Why did it write the number? Surely when it is written afterwards (v. 14), “three cities you shall give…” [Therefore] we see that there were a total of six. Rather, it was to teach that they did not provide refuge until all six were established.

V. 13. והערים וגו׳ שש ערי מקלט תהיינה. Auch die transjordanischen bereits von Mosche bestimmten drei Städte treten nicht früher in Kraft, bis auch die drei im Lande bestimmt sind. Die מקלט-Institution muss gleichzeitig überall im ganzen jüdischen Gebiete in Kraft treten (Mackot 9b). תחיינה לכם (siehe V. 11).