Bava Metzia 64A

בעישורייתא וחומשייתא.

For example: if the money was given in units of tens or fives, it can be assumed that the owner of the money counted the coins in groups of tens or fives and erred in his count.

אמר ליה רב אחא בריה דרבא לרב אשי: ואי איניש תקיפא הוא דלא יהיב מתנה, מאי? אמר ליה: דלמא מיגזל גזליה ואבלע ליה בחשבון. דתניא: הגוזל את חבירו והבליע לו בחשבון ⁠– יצא.

Rav Aḥa, son of Rava, said to Rav Ashi: And if the one who gave the money is a harsh person, who is not accustomed to giving gifts, what is the halakha? Should it be assumed that he made a mistake? Rav Ashi said to him: Perhaps that person once robbed the recipient, and now he included in the calculation the amount he stole, in order to return the stolen money without informing him of the theft. As it is taught in a baraita: One who robs another and then returns the stolen money by including it in the calculation of money paid for another item has fulfilled his obligation to return the stolen money.

ואי איניש דאתי מעלמא, דלא שקיל וטרי בהדיה, מאי? אמר ליה: דלמא איניש אחרינא גזליה, ואמר ליה: כי יזיף פלוני פשיטי מינך ⁠– אבלע ליה בחשבון.

Rav Aḥa, son of Rava, asked Rav Ashi: And if the giver was a person from the outside, with whom the recipient had never conducted business, what is the halakha? Should it be assumed that the additional money was given in error? Rav Ashi said to him: Perhaps another person, an acquaintance of the giver’s, robbed the recipient and said to the giver: When so-and-so borrows money from you, include it in the calculation. It is possible that the one who robbed the recipient chose this manner of restoring the latter’s money in order to be spared any shame.