Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.099.

All words of praise and glory to Allah, extolling His Perfect Attributes of Power and Majesty, Beauty and Sublimeness, whether one utters them by tongue or says them silently in one’s heart, are known as zhikr or remembrance of Allah. He has commanded us to remember Him always and ever. The Qur’an says: O you who believe! Celebrate the praises of Allah, and do so often; and glorify Him morning and evening. Qur’an 33.41

If anyone remembers Allah, He remembers that person: “Remember me, I shall remember you.” Qur’an 2.152 In a hadith qudsi, the Prophet, peace be upon him, narrated: “Allah says: ‘I am to my servant as he expects of Me, I am with him when he remembers Me. If he remembers Me in his heart, I remember him to Myself, and if he remembers me in an assembly, I mention him in an assembly better than his, and if he draws nearer to Me a hand’s span, I draw nearer to him an arm’s length, and if he draws nearer to Me an arm’s length, I draw nearer to him a fathom length, and if he comes to me walking, I rush to him at [great] speed. (Bukhari and Muslim)

Allah has bestowed a special distinction upon those who remember Him. The Prophet, peace be upon him, said, “The devotees have surpassed all.” They asked, “Who are these exceptional people (Mufarridun), O Prophet of Allah?” He replied, “Those men and women who remember Allah unceasingly.” (Muslim) These are the people who are really alive. Abu Musa reported, “The likeness of the one who remembers his Lord and the one who does not remember Him is like that of a living to a dead person.” (Bukhari)

Remembrance of Allah is the foundation of good deeds. Whoever succeeds in it is blessed with the close friendship of Allah. That is why the Prophet, peace be upon him, used to make remembrance of Allah at all times. When a man complained, “The laws of Islam are too heavy for me, so tell me something that I can easily follow,” the Prophet, peace be upon him, told him, “Let your tongue be always busy with the remembrance of Allah.” The Prophet, peace be upon him, would often tell his Companions, “Shall I tell you about the best of deeds, the most pure in the sight of your Lord, about the one that is of the highest order and is far better for you than spending gold and silver, even better for you than meeting your enemies in the battlefield where you strike at their necks and they at yours?” The Companions replied, “Yes, O Messenger of Allah!” The Prophet, peace be upon him, said, “Remembrance of Allah.” (Reported by Tirmizhi, Ahmad, and Al-Hakim, who considers its chain of narrators sound)

Remembrance of Allah is also a means of deliverance from Hell Fire. Mu’azh reported, “The Prophet, peace be upon him, said, ‘No other act of man is a more effective means for his deliverance from the chastisement of Allah than the remembrance of Allah.” (Ahmad) Ahmad reports that the Prophet, peace be upon him, said, “Whatever you say in celebration of Allah’s Glory, Majesty, and Oneness, and all your words of Praise for Him gather around the Throne of Allah. These words resound like the buzzing of bees, and call attention to the person who uttered them to Allah. Don’t you wish to have someone there in the presence of Allah who would call attention to you?”