Musnad Abu Ya'la al-Mawsili 6:15

Musa narrated to us, Muhammad ibn Isma'il ibn Ja'far al-Tahhan narrated to me, Ghassan ibn Bishr al-Kahili narrated to us, from Muslim, from Khaythama, from Sa'd: That the Messenger of Allah (peace be upon him) blocked the doors of the people in the mosque and opened the door of Ali. The people spoke about that, so he said: "I did not open it, but Allah opened it."