TT #200 · Parashas Shoftim · Fifth Aliyah · Passuk 19:04
And this is the matter of the killer who shall flee there and live: one who strikes his fellow without knowledge, and he was not an enemy to him from yesterday and the day before.
Torah Temimah points to Makkot 9a.
TT lemma: וְהוּא לֹא שֹׂנֵא לוֹ.
English: ‘And he was not an enemy to him from yesterday and the day before’ – excluding one who was an enemy.
Derash on the absence of enmity (Bavli) — the verse requires that there was no prior hatred.
If the killer had been an enemy of the victim, the act is not treated as pure accident for the purpose of refuge.