שולחן ערוך
הלוקח טלית מצוייצת אמישראל באו מתגר עכו"ם [ואומר שלקחן גמישראל נאמן] [נ"י הלכות ציצית] כשר דכיון דתגר הוא חזקה שלקחה מישראל דדלא מרע נפשיה אבל אם לקח מעכו"ם שאינו תגר הפסול':
One who buys a tallis that already has its tzitzis attached from a fellow Jew, or from a non-Jewish merchant who deals in such goods, and the merchant says that he acquired them from a Jew — he is believed. (This bracketed ruling is sourced from the Nimukei Yosef, Hilchos Tzitzis.) The tallis is valid to use. For since he is a merchant, there is a presumption that he acquired it from a Jew, because a merchant will not damage his own reputation by lying (were he found out, people would stop trusting his word in his trade). But if one bought it from a non-Jew who is not a merchant, it is invalid.
אין מוכרין טלית מצוייצת ולעכו"ם זשמא יתלוה עם ישראל בדרך ויהרגנו אפי' למשכן ולהפקיד טלית מצוייצת לעכו"ם אסור אא"כ הוא חלפי שעה דליכא למיחש להא:
One may not sell a tallis with its tzitzis attached to a non-Jew, lest, wearing it, he attach himself as a traveling companion to a Jew on the road and then kill him (the Jew, taking the non-Jew for a fellow Jew because of the tzitzis, would trust him). Even to pledge such a tallis as collateral, or to leave it in a non-Jew's safekeeping, is forbidden, unless it is only for a brief, temporary period, in which case there is no concern for this danger.
משנה ברורה
(א) מישראל - אפילו אין מכיר אותו שהוא כשר ונאמן אפ"ה תלינן דסתם ישראל בחזקת כשר הוא ובודאי טוואן ושזרן ותלאן לשמן אם לא שהוא חשוד [ב"ח] וכללי החשוד עיין ביו"ד סימן קי"ט:
Explaining the words of the Shulchan Aruch, "from a Jew": Even if the buyer does not know this Jew to be a person of established integrity and reliability, nevertheless we assume the tzitzis are fit, since an ordinary Jew carries a presumption of being trustworthy in such matters, and we assume he certainly spun, twisted, and attached the threads with the proper intent (lishmah, for the sake of the mitzvah). This holds unless the Jew is known to be suspect in this matter (as noted by the Bach). For the general rules governing who is considered "suspect," see Yoreh De'ah siman 119.
(ב) או מתגר א"י - אפילו אינו מוחזק לקנות טליתות רק מוחזק לקנות שאר סחורות אפ"ה נאמן דאם ימצא בדאי בדבר אחד שוב לא יאמינוהו בד"א:
Explaining "or from a non-Jewish merchant": Even if this merchant is not specifically established as a dealer in talleisim, but is merely known to deal in other kinds of merchandise, he is nonetheless believed when he says he acquired it from a Jew, because a merchant will not lie — if he were found to be a liar in one matter, people would no longer trust him in anything else (and he will not jeopardize his livelihood).
(ג) מישראל נאמן - עיין בלבוש דמוכח מיניה שא"צ התגר לומר שקנה מנאמן דאפילו מסתם ישראל כשר כמו בישראל שקנה מישראל וכן משמע משאר אחרונים ואפשר דגם הרמ"א סובר כן ותיבת נאמן קאי על התגר שהוא נאמן בדיבורו והוסיף הרמ"א זה להורות לנו הסברא דדוקא על דיבורו סמכינן ומאמינין לו דלא מרע נפשיה לומר שקר משא"כ בסתמא לא מרע נפשיה עי"ז:
Explaining "from a Jew — he is believed": See the Levush, from whom it is evident that the merchant need not specify that he bought it from someone of established reliability; rather, even if he bought it from an ordinary Jew it is valid, just as in the case of a Jew who buys from a Jew. And so it is implied by the other Acharonim as well. It is possible that the Rema too holds this view. According to this, the word "believed" refers to the merchant — that he is believed as to his word; and the Rema added this phrase to teach us the underlying reasoning: it is specifically upon his stated word that we rely and believe him, since he will not damage his reputation by lying, whereas when he says nothing at all, he does not thereby damage his reputation (so the leniency rests on his actual statement).
(ד) דלא מרע נפשיה - עיין במ"א שכתב דוקא גבי טלית בציציותיה סמכינן על סברא זו ומאמינין לו משום דאין דרך לנכרי לתלות ציצית בבגדו אבל לקנות ציצית אסור אף מתגר שמא לא היה הטויה והשזירה לשמה וכן פסק הט"ז ודה"ח ויש מקילין בזה ועיין בארה"ח ובישועות יעקב שהסכימו דהיכא דעסק התגר הוא לקנות ציצית מישראל ולמכור מותר מתגר:
Explaining "because he will not damage his own reputation": See the Magen Avraham, who writes that it is specifically regarding a tallis with its tzitzis already attached that we rely on this reasoning and believe him, because it is not the way of a non-Jew to attach tzitzis onto his own garment (so the tzitzis were presumably put on by a Jew). But to buy loose tzitzis threads is forbidden even from a merchant, lest the spinning and twisting were not done lishmah. And so ruled the Taz and the Derech HaChaim. There are, however, those who are lenient in this matter (regarding buying loose threads from a merchant). And see the Aruch HaChaim and the Yeshuos Yaakov, who agreed that where the merchant's business is specifically to buy tzitzis from Jews and resell them, it is permitted to buy from such a merchant.
(ה) פסולה - שמא הוא בעצמו עשה הציצית בהבגד וכ"ש דאסור לקנות ממנו ציצית דשמא לא נטוה לשמה וא"כ פשוט דאפילו אם ירצה להתירם מהבגד ולקשרם מחדש אסור [מ"א ושארי אחרונים דלא כט"ז]. מצא טלית מצוייצת בשוק כשר. ואסור לשלוח ציצית אפילו פסוקין ושזורין ע"י עו"ג אם לא בשני חותמות:
Explaining "it is invalid": lest the non-Jew himself made and attached the tzitzis onto the garment (and a non-Jew's tzitzis are invalid). And all the more so it is forbidden to buy loose tzitzis from him, lest they were not spun lishmah. Therefore it is obvious that even if one wishes to untie the threads from the garment and re-tie them anew, it remains forbidden (so the Magen Avraham and the other Acharonim, against the Taz). If one found a tallis with tzitzis attached lying in the marketplace, it is valid (we assume it belonged to a Jew). And it is forbidden to send tzitzis threads — even ones already cut to length and twisted — by means of a non-Jew, unless they are sealed with two seals.
(ו) לעובד כוכבים - אפילו אם הוא תגר דגם הוא חשוד על שפיכת דמים וג"ע והא דאמרינן לעיל בס"א חזקה שלקחה מישראל וכו' היינו שישראל עבר ומכרה לו:
Explaining "to a non-Jew": Even if the non-Jew is a merchant, the prohibition of selling to him applies, for he too is suspect regarding bloodshed and illicit relations. And that which we said above in se'if 1 — that there is a presumption a merchant acquired it from a Jew — refers to a case where a Jew transgressed and sold it to him (the leniency there is only about the tzitzis being valid, not a license to sell to a non-Jew).
(ז) שמא יתלווה - ועוד איכא טעם בגמרא משום זונה ופירש"י שיתננה לזונה באתננה ותאמר שישראל נתן לה וא"כ כ"ש דאסור למכור לנכרית מטעם זה ועיין בח"א שכתב דלטעם שמא יתלווה ליכא למיחש השתא דאינן חשודים על ש"ד =שפיכות דמים= אבל לטעם דזונה יש לחוש:
Explaining "lest he attach himself as a companion": And there is a further reason given in the Gemara, on account of a harlot, which Rashi explains: lest the non-Jew give the tallis to a harlot as her hire, and she then claim that a Jew gave it to her (bringing the tzitzis into disrepute). If so, all the more so it is forbidden to sell to a non-Jewish woman, for this reason. And see the Chayei Adam, who wrote that as for the reason of "lest he attach himself and kill," nowadays there is no concern, since they are not suspect regarding bloodshed; but as for the reason of the harlot, there is still cause for concern.
(ח) לפי שעה - אבל אם הסיר הציצית אע"פ שנשארו הנקבים מותר אפילו למכור הטלית לנכרי:
Explaining "only for a brief, temporary period": But if one removed the tzitzis — even though the holes remain in the garment — it is permitted even to sell the tallis outright to a non-Jew.