Reference for Menachot 80:8

מיתיבי חסידים הראשונים כיון שארגו בה ג' היו מטילין לה תכלת אימא כיון שפצעו בה ג' היו מטילין לה תכלת

Raba said in the name of R'Sehora who said it in the name of R'Huna, If a man inserted fringes in the corners of a three-cornered garment and then added a fourth corner [and inserted a fringe therein], it is invalid, because of the rule 'Thou shalt make, and not use what is ready made'.<span class="x" onmousemove="('comment',' A three-cornered garment is exempt from zizith, accordingly when the first three fringes were inserted there was no obligation for fringes, and when the obligation falls due, i.e. when the fourth corner is added, the fringes are found to be already made.');">¹²</span> An objection was raised: The pious men of old used to insert the zizith<span class="x" onmousemove="('comment',' Lit., 'the blue' (threads) .');">¹³</span>

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