Reference for Shabbat 223:5
מנעל אמנעל לא קשיא הא דקתני חייב חטאת בדאושכפי פטור אבל אסור בדרבנן מותר לכתחלה בדבני מחוזא
[The rulings on] sandals too are not contradictory: when it states that 'one is liable to a sin-offering', it refers to [sandals] of travellers<span class="x" onmousemove="('comment',' Taya'a, specially Arabian caravan merchants. ');"><sup>10</sup></span> tied by cobblers; one is not liable yet it is forbidden', refers to amateur knots<span class="x" onmousemove="('comment',' Lit., 'balls'. ');"><sup>11</sup></span> tied by [the wearers] themselves; 'it is permitted at the outset', refers to sandals in which two go out,<span class="x" onmousemove="('comment',' They are worn by two different people on occasion. Hence they must be tied exactly each time, and therefore the knot is temporary. — In the other two the differences are the same as in the case of shoes. ');"><sup>12</sup></span>