Responsa for Bava Kamma 208:16
וכי איכא אחריות נכסים מאי הוי מלוה על פה היא ומלוה על פה אינו גובה לא מן היורשין ולא מן הלקוחות
said to him: Did the Master mean to say Yesh Talmud [i.e. there is a definite teaching on this subject] or did the Master mean to say Yishtallemu [i.e., it stands to reason that the heirs should have to pay]? He replied to him: I said Yesh Talmud [i.e. there is a definite teaching on the subject] as I maintain that this could be amplified from the [added] Scriptural expressions.<span class="x" onmousemove="('comment',' From the objects of payment enumerated in detail in Lev. V, 23. But if no admission whatever was made why should even the principal be paid? ');"><sup>27</sup></span> — It must therefore be said that what was meant by the statement 'he made no admission' was that the father made no admission though the son did. But why should the son not become liable to pay even a Fifth for his own oath?<span class="x" onmousemove="('comment',' When he took it falsely. ');"><sup>28</sup></span>
Teshuvot Maharam
A. Even A's producing a written consent from the widow would be of no avail unless he can also prove through witnesses that the widow instructed and ordered the writing of the instrument. Should he not be able to do so, he will have to remove the building from the widow's premises and pay her rent for the time his building stood thereon. Should A produce such witnesses, his contract with the widow's son and son-in-law will be non-voidable even though A did not yet pay the rent for the full ten years. Although the widow did not personally instruct her son and son-in-law to rent her premises to A, but sent such instructions in writing — such manner of sending instructions not being acceptable in talmudic law — nevertheless the son and son-in-law became the widow's agents, since it is the usual custom of merchants to accept as valid written instruments, and since the custom of merchants prevails in business transactions.
This Resp. is addressed to R. Eliezer ha-Kohen, and R. Eliezer.
SOURCES: Pr. 698.