so that he will not trouble me later by constantly demanding the money.

The Gemara attempts to bring a proof in support of the opinion of Abaye and Rava from what we learned in the mishna (5a): If after the wall was built one of the neighbors claims he alone constructed it and the other did not participate in its building, the latter is nevertheless presumed to have given his share of the money, unless the claimant brings proof that the other did not give his part.

The Gemara clarifies the matter: What are the circumstances of the case under discussion? If we say that he said to him: I paid you at the time when the payment became due, when the wall was completed, it is obvious that he is presumed to have given his part. Rather, is it not that he said to him: I paid you within the time before the payment became due, while the wall was still under construction? And with regard to such a case the mishna states that he is presumed to have given his share. Apparently, a person is apt to repay his debt within its time, in accordance with the opinion of Abaye and Rava. The Gemara rejects this proof: Here it is different, because the time to pay is upon the completion of each and every row. Payment does not become due specifically at the completion of the entire wall.

The Gemara further suggests: Come and hear a proof in support of the opinion of Reish Lakish from the continuation of the mishna (5a): The court does not obligate the reluctant neighbor to contribute to the building of the wall higher than four cubits. But if the reluctant neighbor built another wall close to the wall that had been built higher than four cubits, in order to set a roof over the room that was thereby created, the court imposes upon him the responsibility to pay his share for all of the rebuilt wall, even though he has not yet set a roof over it. If the builder of the first wall later claims he did not receive payment from his neighbor, the neighbor is presumed not to have given his share of the money, unless he brings proof that he did in fact give money for the building of the wall.

The Gemara clarifies the matter: What are the circumstances of the case under discussion? If we say that he said to him: I paid you at the time that the payment became due, when the wall was completed, why is he not deemed credible? Rather, is it not that he said to him: I paid you within the time before the payment became due, and therefore he is not deemed credible? Apparently, a person is not apt to repay his debt within its time, in accordance with the opinion of Reish Lakish. The Gemara rejects this proof: Here it is different, since the reluctant neighbor says: Who says that the Rabbis will obligate me to pay for this wall? In such a case he certainly does not pay before the payment becomes due.

Rav Pappa and Rav Huna, son of Rav Yehoshua, acted in such a case in accordance with the opinion of Abaye and Rava. Mar bar Rav Ashi acted in accordance with the opinion of Reish Lakish. The Gemara concludes: And the halakha is in accordance with the opinion of Reish Lakish that one is not deemed credible when he says that he repaid a loan before it became due. And if the debtor dies, the court collects payment even from his orphans based on this assumption. And even though the Master said that one who comes to collect money from the property of orphans cannot collect unless he first takes an oath that he did not already collect the debt from the deceased, here he can collect without taking an oath because there is a presumption that a person is not apt to repay his debt within its time.

A dilemma was raised before the Sages: What is the halakha if the lender stipulated a time with the borrower for repayment of the debt, and he demanded payment of the money after the time that the payment became due had passed, and the borrower said to him: I already repaid you within the time before the payment became due? Do we say that even where there is a presumption against someone’s claim, as in this case where there is a presumption that people do not pay their debts before they become due, we say that the borrower can claim: Why would I lie? If one of the litigants could have advanced a claim more advantageous to his cause than the one he actually did, the assumption is that he is telling the truth. Consequently, in this case had the borrower wished to lie, he could have said that he repaid his debt when it became due, and he would have been deemed credible. Therefore, when he claims that he repaid it before it came due he should also be deemed credible.