יורה דעה ש״בYoreh De'ah 302

Se’if 1א׳

בֶּגֶד צֶמֶר שֶׁאָבַד בּוֹ חוּט שֶׁל פִּשְׁתָּן אוֹ בֶּגֶד פִּשְׁתָּן שֶׁאָבַד בּוֹ חוּט שֶׁל צֶמֶר, צוֹבְעוֹ, שֶׁאֵין הַצֶּמֶר וְהַפִּשְׁתָּן עוֹלִים בְּצֶבַע אֶחָד וּמִיָּד הוּא נִכָּר לוֹ וְשׁוֹמְטוֹ, וְאִם לֹא נִכָּר, הֲרֵי זֶה מֻתָּר, שֶׁמָּא נִשְׁמַט וְהָלַךְ לוֹ, שֶׁהֲרֵי בָּדַק וְלֹא מְצָאוֹ. בַּמֶּה דְּבָרִים אֲמוּרִים, בְּכִלְאַיִם דְּרַבָּנָן. אֲבָל בְּכִלְאַיִם דְּאוֹרַיְתָא, אֵין הוֹלְכִין לְהָקֵל בִּסְפֵקָן (טוּר).

A woollen garment in which a thread of linen was lost, or a linen garment in which a thread of wool was lost — he dyes it, for wool and linen do not take one dye, and at once it is recognisable to him and he pulls it out. And if it is not recognisable, it is permitted, for perhaps it slipped out and went its way, since he examined and did not find it. When is this said? With kilayim (the forbidden mixture of wool and linen) by rabbinic law. But with kilayim by Torah law, we do not follow leniency in their doubt (Tur).

Se’if 2ב׳

הַלּוֹקֵחַ כְּלֵי צֶמֶר מֵהַגּוֹיִים, צָרִיךְ לְבָדְקָן יָפֶה יָפֶה, שֶׁמָּא הֵם תְּפוּרִים בְּפִשְׁתָּן. וְהַקּוֹנֶה בְּגָדִים מִן הָעוֹבֵד כּוֹכָבִים, צָרִיךְ לְהַתִּיר תְּפִירָתָן וּלְתָפְרָן בְּקָנַבּוֹס (טוּר) וְאֲפִלּוּ אִם הָעוֹבֵד כּוֹכָבִים מֵסִיחַ לְפִי תֻּמּוֹ שֶׁתְּפָרָן בְּקַנַּבּוֹס, אֵינוֹ נֶאֱמָן. וּבִמְקוֹמוֹת שֶׁהַפִּשְׁתָּן בְּיֹקֶר מִן הַקַנַּבּוֹס, יֵשׁ לִסְמֹךְ לְהַתִּיר. הַגָּה: וְאָסוּר לוֹמַר לְעוֹבֵד כּוֹכָבִים לִתְפֹּר לוֹ בְּגָדִים בְּחוּטֵי קַנַּבּוֹס, אַף עַל פִּי שֶׁפִּשְׁתָּן יוֹתֵר בְּיֹקֶר, דְּנָקֵל לִתְפֹּר בְּפִשְׁתָּן מִבַּקַנַּבּוֹס (רַשְׁבָּ"א סִימָן תשס"א). אֲבָל אִם נוֹתֵן לוֹ חוּטֵי קַנַּבּוֹס, שָׁרֵי, וְלֹא חַיְשִׁינָן לְאַחְלוּפֵי, מֵאַחַר שֶׁיֵּשׁ לַעֲמֹד עַל הַדָּבָר, שֶׁחוּטֵי פִּשְׁתָּן כְּשֶׁמַּדְלִיק כָּבֵה מַהֵר, וְשֶׁל קַנַּבּוֹס הוֹלֵךְ וְשׂוֹרֵף (כֵּן מַשְׁמָע במ"מ פ"ח דמ"א). וְכֵן נוֹהֲגִין, אַף עַל פִּי שֶׁיֵּשׁ מַחְמִירִין (רַשְׁבָּ"א הַנַּ"ל). וְיִשְׂרָאֵל הֶחָשׁוּד לִתְפֹּר כִּלְאַיִם, דִּינוֹ כְּעוֹבֵד כּוֹכָבִים. יֵשׁ מַחְמִירִין דְּלֹא יִתְפֹּר בֶּגֶד צֶמֶר בְּקַנַּבּוֹס לָבָן, שֶׁלֹּא יַחְשְׁדוּהוּ שֶׁהוּא פִּשְׁתָּן, וְלָכֵן צוֹבְעִין הַקַנַּבּוֹס. (מהרי"ל).

One who buys woollen garments from the gentiles must examine them very thoroughly, lest they are sewn with linen. And one who buys garments from an idolater must unpick their sewing and sew them with hemp (Tur); and even if the idolater says, speaking in his innocence (mesiach lefi tumo — one who tells of a thing in passing, with no thought of giving testimony), that he sewed them with hemp, he is not believed. And in places where linen is dearer than hemp, one may rely on this to permit. Hagah [Rema]: And it is forbidden to tell an idolater to sew garments for him with threads of hemp, even though linen is dearer, for it is easier to sew with linen than with hemp (the Rashba, siman 761). But if he gives him threads of hemp, it is permitted, and we are not concerned for an exchange, since the matter can be ascertained: threads of linen, when one lights them, go out quickly, while those of hemp go on burning (so it is implied in the Maggid Mishneh, chapter 8 of the Laws of Forbidden Foods). And so is the practice, even though there are those who are stringent (the Rashba cited above). And an Israelite who is suspected of sewing kilayim — his law is as an idolater's. There are those who are stringent that one should not sew a woollen garment with white hemp, lest they suspect him that it is linen; and therefore they dye the hemp (Maharil).