Sayyiduna Awf bin Malik (may Allah be pleased with him) entered the mosque leaning on Dhu al-Kala', while Ka'b was preaching to the people. Sayyiduna Awf (may Allah be pleased with him) said to Dhu al-Kala': Will you not stop this nephew of yours from what he is doing? For I heard the Messenger of Allah (peace and blessings be upon him) say: "None should preach to the people except a ruler, or one appointed by the ruler, or a vain person."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15212