Shaytan's Hand on the Heart

Two further hadith of the Prophet (peace be upon him) complete the matter. Inna al-shayṭāna wāḍiʿun khaṭmahu ʿalā qalbi ibni Ādam, fa-in dhakara Allāha khanasa, wa in nasiya iltaqama qalbah: in this hadith the Prophet (peace be upon him) says that Shayṭān, the accursed, every day, through the power given to him by Allah (swt), puts his network, his net, shabakah, onto the heart of the believer — whispering, waswasah, thoughts of every kind. If the servant of Allah, as soon as he wakes up, for example, starts with the remembrance of Allah (swt), beginning right early in the morning, Shayṭān removes his net from the heart of the Muslim. But if he forgets to make dhikr of Allah (swt), Shayṭān holds on to his heart, and it comes under the control and influence, taʾthīr, of Shayṭān, the accursed.

In a different hadith the Prophet (peace be upon him) says that he who abandons dhikr — the commentators explain: who does not remember Allah (swt) constantly — shall be removed from īmān, from true faith. And again, in a ḥadīth qudsī, the Messenger of Allah (peace be upon him) narrates that Allah said to him: O son of Adam, when you make dhikr of Me, when you remember Me, you have indeed shown your gratitude, you have praised Me, you are thankful to Me; and when you stop making dhikr of Me, you have completely covered over the truth of Me. In other words, one who does not make dhikr of Allah (swt) has removed himself, has fallen into kufr itself. There are literally thousands and thousands of hadith of the Messenger of Allah (peace be upon him) in this regard, and there is more that could be said of them.