Imam Malik (may Allah have mercy on him) was informed that a man asked Qasim bin Muhammad bin Abi Bakr as-Siddiq: "I experience doubts in prayer, and I experience them a lot." So Qasim said: "Go and perform your prayer, and do not pay attention to the doubts, for the doubt will never leave you until you finish the prayer and have in your heart the thought that you have completed the whole prayer."