Reference for Yevamot 204:6
אי נעל נעל ריבה אפי' כל מילי נמי אם כן תחש מאי אהני ליה
applying only to the permissibility [of the woman] to strangers,<span class="x" onmousemove="('comment',' Lit., 'to the world'. Only for this purpose is intention a sine qua non. ');"><sup>14</sup></span> but to the brothers she does become forbidden.<span class="x" onmousemove="('comment',' Even where there was no intention but mere action. ');"><sup>15</sup></span> Rab Judah stated in the name of Rab: No <i>halizah</i> may be performed with a sandal that was sewn with flax,<span class="x" onmousemove="('comment',' I.e., provided with a flax lining or, according to another interpretation, stitched with a flaxen thread (cf. Rashi). ');"><sup>16</sup></span> for it is said in Scripture, And I shod thee with tahash.<span class="x" onmousemove="('comment',' Ezek. XVI, 10, E.V. sealskin. The tahash, the skin of which was used for one of the coverings of the roof of the Tabernacle made by Moses in the wilderness, formed a class of its own, and the Sages could not determine whether it belonged to the class of wild or of domestic animals (cf. Shab. 28b). The mention in the context of shoeing of tahash, the use of the skin of which only was recorded in the Scriptures, is taken to imply that the shoe spoken of in the Scriptures was invariably made of a material similar to that of the skin of tahash, viz., leather. Hence the inadmissibility in halizah of any shoe that was not wholly made of leather. ');"><sup>17</sup></span>