Midrasch zu Bamidbar 35:26

(Bamidbar 35:26) "And if the murderer go beyond the border of the city of refuge … (27) the avenger may slay the murderer": R. Elazar b. Azaryah said: If under the measure of punishment, the lesser (of the two measures), one who steps one step (beyond the permitted limits) is liable for his soul, then under the measure of reward, the greater, how much more so (is his soul ennobled by an "extra step" for a mitzvah)! (37) "And the avenger find him": any man (i.e., not only the literal "blood-avenger," his kin). (38) "For in the city of his refuge shall he dwell": whence it is derived: If one killed in that city (to which he had been exiled), he is exiled from one neighborhood (in that city) to another. And a Levite (who lives in a city of refuge) is exiled from that city to another. "and after the death of the high-priest, the slayer shall return to the land of his holding": but not to his (previous high) position. These are the words of R Yehudah. R. Meir says: even to his position.