Sefer Chasidim Siman 90
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זכין לאדם שלא בפניו מעשה באיש אחד שהיה תמיד מעיין בטליתות של בית הכנסת לראות אם נקרעו או נתקלקלו חוטי הציצית והיה מצייצה כהלכתה והיה מודיע לבעל הטלית:
Medieval Jewish mysticism, translated by Sholom Alchanan Singer. Northbrook, Ill. Whitehall Co., 1971
You may obtain privilege in behalf of a person in his absence.¹ (And so) it happened with a certain person who constantly examined the prayer shawls in the House of Assembly, to see if they were torn or if the fringes had deteriorated. He inserted the fringes according to law and would then notify the owner of the prayer shawl.²
footnotes: ¹ Ketuboth 11a. ² Shabbath 10a.