יורה דעה ש״גYoreh De'ah 303

Se’if 1א׳

הָרוֹאֶה כִּלְאַיִם שֶׁל תּוֹרָה עַל חֲבֵרוֹ, אֲפִלּוּ הָיָה מְהַלֵּךְ בַּשּׁוּק, הָיָה קוֹפֵץ לוֹ וְקוֹרְעוֹ מֵעָלָיו מִיָּד, וַאֲפִלּוּ הָיָה רַבּוֹ. וְיֵשׁ אוֹמְרִים דְּאִם הָיָה הַלּוֹבֵשׁ שׁוֹגֵג, אֵין צָרִיךְ לוֹמַר בַּשּׁוּק, דְּמִשּׁוּם כְּבוֹד הַבְּרִיּוֹת יִשְׁתֹּק, וְאַל יַפְרִישֶׁנּוּ מִשּׁוֹגֵג (טוּר בְּשֵׁם הָרֹא"שׁ). וְאִם הָיָה שֶׁל דִּבְרֵיהֶם, אֵינוֹ קוֹרְעוֹ מֵעָלָיו וְאֵינוֹ פּוֹשְׁטוֹ בַּשּׁוּק, עַד שֶׁמַּגִּיעַ לְבֵיתוֹ. וְכֵן בְּבֵית הַמִּדְרָשׁ אֵין צָרִיךְ לְמַהֵר לָצֵאת (טוּר). וְאִם הָיָה שֶׁל תּוֹרָה, פּוֹשְׁטוֹ מִיָּד.

One who sees kilayim (the forbidden mixture of wool and linen) of the Torah on his fellow, even if he was walking in the market, springs upon him and tears it off him at once, and even if he was his teacher. And some say that if the wearer was acting in error, one need not tell him in the market, for on account of human dignity he should keep silent, and not separate him from his error (Tur in the name of the Rosh). And if it was of their words, he does not tear it off him, and he does not strip it off in the market, until he reaches his house. And likewise in the house of study he need not hurry to go out (Tur). And if it was of the Torah, he strips it off at once.

Se’if 2ב׳

אָסוּר לְהַלְבִּישׁ אֶת חֲבֵרוֹ כִּלְאַיִם.

It is forbidden to clothe one's fellow in kilayim.