Musannaf Ibn Abi Shaybah 31055 — Book of the Judgments

Sayyiduna Ali (may Allah be pleased with him) said: The Prophet (peace and blessings be upon him) sent me to the people of Yemen as a judge so that I would judge between them. I said: "O Messenger of Allah (peace and blessings be upon him)! I have no knowledge of judging." So the Prophet (peace and blessings be upon him) struck his blessed hand on my chest and said: "O Allah, guide his heart and keep his tongue straight." Sayyiduna Ali (may Allah be pleased with him) said: After that I never had a doubt about any judgment between two people, up to the time I sat in this seat of mine.