Deuteronomy 19:6

Otherwise, the avenger of blood might pursue the manslayer in a rage, overtake him if the distance is great, and strike him dead though he did not deserve to die, since he did not intend any harm.

Lest the avenger of the blood pursue the slayer, while his heart is hot, and overtake him, because the way is long, and slay him; whereas he was not worthy of death, inasmuch as he hated him not in time past.