Musnad Abu Ya'la al-Mawsili 3:323

Abu Khaythama narrated to us, Jarir narrated to us, from Mansur, from Rib'i, from Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A servant does not believe until he believes in four things: that there is no god but Allah alone, with no partner, and that I am the Messenger of Allah whom He sent with the truth; and he believes in the resurrection after death; and he believes in the Decree (al-Qadar)."