The Talmud states that one who strikes another person (even without causing injury) transgresses a biblical prohibition: 'You shall not add' — the rabbis derive from this that striking a fellow Jew is absolutely forbidden, calling it an act of wickedness.
אָמַר רַבִּי חֲנִינָא: גּוֹי שֶׁהִכָּה אֶת יִשְׂרָאֵל חַיָּיב מִיתָה, שֶׁנֶּאֱמַר: ״וַיִּפֶן כֹּה וָכֹה וַיַּרְא כִּי אֵין אִישׁ [וַיַּךְ אֶת הַמִּצְרִי] וְגוֹ׳״. וְאָמַר רַבִּי חֲנִינָא: הַסּוֹטֵר לוֹעוֹ שֶׁל יִשְׂרָאֵל כְּאִילּוּ סוֹטֵר לוֹעוֹ שֶׁל שְׁכִינָה, שֶׁנֶּאֱמַר: ״מוֹקֵשׁ אָדָם יָלַע קֹדֶשׁ״. מַגְבִּיהַּ, עַבְדּוֹ, שָׁבַת – סִימָן. אָמַר רֵישׁ לָקִישׁ: הַמַּגְבִּיהַּ יָדוֹ עַל חֲבֵירוֹ, אַף עַל פִּי שֶׁלֹּא הִכָּהוּ, נִקְרָא רָשָׁע, שֶׁנֶּאֱמַר: ״וַיֹּאמֶר לָרָשָׁע לָמָּה תַכֶּה רֵעֶךָ״. ״לָמָּה הִכִּיתָ״ לֹא נֶאֱמַר, אֶלָּא ״לָמָּה תַכֶּה״ – אַף עַל פִּי שֶׁלֹּא הִכָּהוּ נִקְרָא רָשָׁע. אָמַר זְעֵירִי אָמַר רַבִּי חֲנִינָא: נִקְרָא חוֹטֵא, שֶׁנֶּאֱמַר: ״וְאִם לֹא לָקַחְתִּי בְחׇזְקָה״, וּכְתִיב: ״וַתְּהִי חַטַּאת הַנְּעָרִים גְּדוֹלָה מְאֹד״. רַב הוּנָא אָמַר: תִּיקָּצֵץ יָדוֹ, שֶׁנֶּאֱמַר: ״וּזְרוֹעַ רָמָה תִּשָּׁבֵר״. רַב הוּנָא קַץ יְדָא.
Rabbi Ḥanina says: A gentile who struck a Jew is liable to receive the death penalty, as it is stated when Moses saw an Egyptian striking a Hebrew: “And he turned this way and that way, and when he saw that there was no man, he struck the Egyptian and hid him in the sand” (Exodus 2:12). And Rabbi Ḥanina says: One who slaps the cheek of a Jew is considered as though he slapped the cheek of the Divine Presence; as it is stated: “It is a snare [mokesh] for a man to rashly say [yala]: Holy” (Proverbs 20:25). The verse is interpreted homiletically to mean: One who strikes [nokesh] a Jew is considered as though he hurt the cheek [lo’a] of the Holy One. The Gemara states a mnemonic for the upcoming statements of Reish Lakish: Raises, his slave, Shabbat. Reish Lakish says: One who raises his hand to strike another, even if he ultimately does not strike him, is called wicked, as it is stated: “And two men of the Hebrews were struggling with each other, and he said to the wicked one: Why should you strike your friend?” (Exodus 2:13). The phrase: Why did you strike, is not stated, but rather: “Why should you strike,” indicating that one who raised his hand to strike another, even if he ultimately did not strike him, is called wicked. Ze’eiri says that Rabbi Ḥanina says: One who raises his hand to strike another is called a sinner; as it is stated: “And the priest’s lad would come…and would say to him, but you shall give now, and if not, I will take by force” (I Samuel 2:15–16), and it is written with regard to this behavior: “And the sin of the youths was very great” (I Samuel 2:17). Rav Huna says: His hand should be cut off, as it is stated: “And the high arm shall be broken” (Job 38:15). If one habitually lifts his arm to strike others, it is better that it be broken. The Gemara relates that Rav Huna cut off the hand of a person who would habitually hit others.