Reference for Bava Batra 11:3
ת"ש מד' אמות ולמעלה אין מחייבין אותו סמך לו כותל אחר כו' עד שיביא ראיה שנתן
Come and hear: FOR REBUILDING HIGHER THAN FOUR CUBITS NEITHER CAN BE COMPELLED [TO CONTRIBUTE]. IF, HOWEVER, HE BUILDS ANOTHER WALL CLOSE TO IT … UNTIL HE ADDUCES PROOF THAT HE HAS GIVEN. How are we to understand this? Are we to suppose that the claim is made some time after and the defendant pleads, I paid you when the money fell due? If so, why [should we] not [believe him]? We must suppose therefore that he pleads, I paid you before the time of payment, [and yet he has to contribute]; which would show [would it not] that where there is a presumption [against him], we do not plead [on his behalf], What motive has he to tell a lie? — Here the case is different, because he can say to himself, How do I know that the Rabbis will compel me to pay?<span class="x" onmousemove="('comment',' V. p. 19 n. 7. ');"><sup>3</sup></span>