Reference for Nedarim 96:6
זימנין אמר ליה משום דסעודתו מוכחת עליו וזימנין אמר ליה ר' אליעזר היא דאמר אפילו ויתור אסור במודר הנאה
ruled, This is a case of 'Acquire, in order to give possession,' and such does not give a legal title. R. Nahman said: He [the son] acquires [it], for [the giving of] a sudarium too is a case of 'Acquire, in order to give possession.'<span class="x" onmousemove="('comment',' One of the methods of acquisition was by exchange (halifin), in which an object (a sudarium kerchief) was given by the purchaser or recipient to the vendor or donor as a symbolical substitute v. B.M. 47a. Now, actually. this was given merely in order that the latter might give legal possession to the former, and was generally returned, yet it was valid. ');"><sup>6</sup></span>