Parashas Shemos · Passuk 2:13
Chabad.org — English translation + Rashi
Torah Temimah points to Sanhedrin 58b (verified).
Sefaria — Exodus 2:13
Sefaria — Sanhedrin 58b
E-Daf — Sanhedrin 58b
English: “And he said to the wicked one” — Reish Lakish said: One who raises his hand against his fellow, even though he has not [yet] struck him, is called wicked, as it is said, “Why do you strike (takeh) your fellow?” — it does not say “why did you strike,” but “why do you [intend to] strike.”
On the daf / in context: See the cited source for the full section.
Custom
Chazal teach that raising a hand to strike is itself enough to be labeled wicked, even before the blow lands.