Musnad Abu Ya'la al-Mawsili 6:67

Abu Khaythama narrated to us, Sulayman ibn Dawud al-Hashimi narrated to us, Yusuf ibn al-Majishun narrated to us, Muhammad ibn al-Munkadir informed me, from Sa'id ibn al-Musayyib, from 'Amir ibn Sa'd, from his father Sa'd, that the Messenger of Allah (may Allah bless him and grant him peace) said to 'Ali: "You are to me in the position of Aaron to Moses, except that there is no prophet after me." Sa'id said: I wanted to hear this directly from Sa'd, so I met him and mentioned to him what 'Amir had mentioned to me. He said: "Yes, I heard it." I said: "You heard it?" He then put his two fingers into his ears and said: "Yes, and if not, may they both go deaf."