Deuteronomy 19:4
And this is the case of the slayer, which shall flee thither, that he may live: Whoso killeth his neighbour ignorantly, whom he hated not in time past; (Deuteronomy 19:4)
Ignorantly.
 That is, “unintentionally,” literally, “without knowledge” (Deut. 4:42; Joshua 20:3, 5).
Hated not.
 The man responsible had acted unintentionally (see Num. 35:23). To require the life of such an unintentional slayer would be to shed innocent blood.