Once, Rav Shabsi HaCohen, the Shach — author of the Sifsei Cohen on the Yoreh De’ah and Choshen Mishpat – had a dispute with a prominent merchant of Vilna. The matter pertained to a monetary transaction, and each claimed loss and damages.
They decided to take the case to Rav Avraham-Aba, who lived in a distant city.
Before they started out, the Shach reviewed all the points of his case in accordance with the Talmud, Rambam, Tur and the Shulchan Aruch, and he was convinced that his arguments were superior and that he would win the case.
Rav Avraham-Aba heard both sides and then found in favor of the Shach’s opponent.
The Shach was dumbfounded. “Surely, you must be mistaken,” he said. “I have reviewed my case and I find that in accordance with the Torah I have to be right. Will you please tell me on what source you based your decision?”
The elderly rav approached his bookcase and took out the sefer, Sifsei Cohen on the Choshen Mishpat, which the Shach had authored the previous year and which was acclaimed throughout the world. He then turned to one of the pages on which the Shach discussed a similar case. Pointing to it, he said, “I based my verdict on this decision established by the Shach.”
Looking into the subject, the Shach saw that the rav was right. The previous year he had discussed a similar case and awarded the decision to the other party.
Revealing his identity, the Shach then exclaimed: “Look how great are the words of our sages who declared (Shabbos 119a), ‘A person never sees nor finds fault with himself!’ ”