Rashi on Deuteronomy 25:3/רש"י על דברים כ״ה:ג׳

1לא יסיף HE SHALL NOT EXCEED — From here is derived the prohibition referring to one who strikes his fellow man (Sanhedrin 86b; cf. Ketubot 33a).

2ונקלה אחיך WHEN THY BROTHER SHOULD SEEM VILE [UNTO THEE] — All the time it has been calling him “wicked” (vv. 1 and 2), but as soon as he has received the lashes it calls him “thy brother”! (Sifrei Devarim 286:14).