Shaikh Uthaimeen, may Allaah have mercy on him, said, “Guard strictly [the practice] of always inspecting/investigating your heart. For it may have the sickness of doubts or the sickness of desires, and everything–and all praise is for Allaah–has a cure. So the Noble Quraan is a cure for doubts and desires.”

Ash-Sharh al-Mumti, vol. 4, p. 22.