Question 516: Some people say, “Indeed, Allaah is aware of what is in the hearts.” Is this saying correct? Was it circulated among the Salaf (righteous predecessors, may Allaah be pleased with them)?
Answer: It is correct to say, “Allaah is aware of what is in the hearts.” Allaah (Exalted be He) said,…and Allaah is All-Knower of what is in (your) breasts. He also said, Allaah knows what is in your hearts. And Allaah is Ever All-Knowing, Most Forbearing.... read more here.