His statement: "Indeed in that is a reminder for whoever has a heart," meaning: the believer, "or listens attentively while he is present [in mind]." The interpretation of Mujahid: Or he lends his ear while his heart is present.
Muhammad said: The meaning is: he listens to the Book of Allah while his heart and understanding are present, not being heedless or absent-minded, and this is what Mujahid intended.