It is narrated from Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "A servant cannot be a believer until he believes in four things: that he bears witness that there is no god but Allah and that I am the Messenger of Allah whom He has sent with the truth; that he has certainty in the resurrection after death; and that he believes in destiny (qadar)." This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim). Some of the students of Imam al-Thawri fell short in narrating it, but in our view that is of no significance.