Sayyiduna Umar (may Allah be pleased with him) said to Sayyiduna Ka'b (may Allah be pleased with him): I want to ask you something, you must not hide anything from me. Sayyiduna Ka'b (may Allah be pleased with him) said: By Allah! I will not hide anything from you of what I know. Sayyiduna Umar (may Allah be pleased with him) said: What do you fear most for the Ummah of Muhammad (peace and blessings be upon him)? He said: Misguiding rulers. Sayyiduna Umar (may Allah be pleased with him) said: You have spoken the truth, the Messenger of Allah (peace and blessings be upon him) told me this confidentially.