It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "No person can be a complete believer until he believes in four things: he bears witness that there is no deity except Allah, and that I am the Messenger of Allah, He has sent me as a true Prophet, he believes in being raised after death, and he believes in destiny."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 758
Hadith Gradingحکم دارالسلام:إسناده صحيح، قاله أحمد شاكر