Reference for Menachot 77:2

ואמר רבה שמע מינה קשר עליון דאורייתא דאי ס"ד דרבנן מאי איצטריך למישרי סדין בציצית פשיטא התוכף תכיפה אחת אינו חיבור אלא שמע מינה דאורייתא

for should you say it is a Rabbinic ordinance,<span class="x" onmousemove="('comment',' But by Biblical law it is not necessary to tie the threads together, not even to the garment.');">⁴</span> then why was it necessary for the Torah to permit the insertion of [woollen] fringes in a [linen] garment?<span class="x" onmousemove="('comment',' This is established by the juxtaposition of the texts, viz., (Deut. XXII, 12) Thou shalt not wear a mingled stuff, wool and limen together, and');">⁵</span> One would have no doubt about it, for if one merely fastens together [two pieces] with one fastening<span class="x" onmousemove="('comment',' I.e., joining cloths of wool and of linen with a single stitch or knot.');">⁶</span>

Jastrow