Abdul Jabbar Khawlani (may Allah be pleased with him) says that once a companion (may Allah be pleased with him) entered the mosque while Ka'b Ahbar (may Allah have mercy on him) was delivering a sermon. He asked, "Who is this?" The people informed him, "This is Ka'b, who is delivering a sermon." He said, "I heard the Prophet (peace and blessings of Allah be upon him) say that only the leader may deliver a sermon, or one who has been given permission, or a show-off." When Ka'b (may Allah have mercy on him) learned of this, he was not seen delivering sermons after that.