Reference for Menachot 70:1

וא"נ כל היכי דכי מיתלי ביה במתנא אתייה אבתריה חדתתא ואידך עתיקתא

Or else, if when one holds up the strap, [the box] hangs on to it,<span class="x" onmousemove="('comment',' And does not snap. o,raeu o, raeu');">¹</span> it is new; otherwise it is old. Abaye was once sitting before R'Joseph when the strap of his tefillin suddenly snapped.

Jastrow