Bava Batra 5B

כי היכי דלא ליטרדן.

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

תנן: בחזקת שנתן, עד שיביא ראיה שלא נתן.

The Talmud attempts to bring a proof in support of the opinion of Abaye and Rava from what we learned in the Mishnah (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.

היכי דמי? אילימא דאמר ליה: ״פרעתיך בזמני״, פשיטא בחזקת שנתן! אלא לאו דאמר ליה: ״פרעתיך בתוך זמני״? אלמא עביד איניש דפרעיה בתוך זמניה! שאני הכא, דכל שפא ושפא זימניה הוא.

The Talmud 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 Mishnah 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 Talmud 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.

תא שמע: בחזקת שלא נתן, עד שיביא ראיה שנתן.

The Talmud further suggests: Come and hear a proof in support of the opinion of Reish Lakish from the continuation of the Mishnah (5a): The court does not obligate the reluctant neighbor to contribute to the building of the wall higher than 4 cubits. But if the reluctant neighbor built another wall close to the wall that had been built higher than 4 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.