THikr of Allah SWT is the most excellent act of Allah's servants and is stressed over a hundred times in the Noble Qur'an. It is the most praiseworthy work to earn Allah's pleasure, the most effective weapon to overcome the enemy, and the most deserving of deeds in reward. It is the flag of Islam, the polish of hearts, the essence of the science of faith, the immunization against hypocrisy, the head of worship, and the key of all success.
There are no restrictions on the modality, frequency, or timing of Dhikr whatsoever. The restrictions on modality pertain to certain specific obligatory acts that are not the issue here, such as Salaah. The Shari'ah is clear and everyone knows what he or she has to do. Indeed, Rasulullah SAW said that the People of Paradise would only regret one thing: not having made enough Dhikr in the world! Are not those who are making up reasons to discourage others from making Dhikr afraid of Allah SWT in this tremendous matter?
Allah SWT says in His Noble Qur'an: "O Believers make abundant mention of ALLAH!" (33:41) And He mentions of His servants "Those who remember their Lord standing, and sitting, and lying on their sides" (3:191), in other words at all times of the day and night. He said (3:190-191): " The creation of heaven and earth and the changes of night and day are signs for people who have wisdom: -- consider who is described as having wisdom -- Those who remember (and recite and call) Allah standing up, sitting, and lying on their sides." `A'isha RA said, as narrated by Muslim, that the Prophet mentioned/remembered Allah at all times of the day and night.
The Prophet said: "If your hearts were always in the state that they are in during dhikr , the angels would come to see you to the point that they would greet you in the middle of the road." Muslim narrated it. Imam Nawawi in his Sharh sahih muslim commented on this hadith saying: "This kind of sight is shown to someone who persists in meditation (muraqaba) , reflection (fikr) , and anticipation (iqbal) of the next world." Mu`adh ibn Jabal RA said that Rasulullah SAW also said: "The People of Paradise will not regret except one thing alone: the hour that passed them by and in which they made no remembrance of Allah." Narrated by Bayhaqi in Shu`ab al-iman (1:392 #512-513) and by Tabarani. Haythami in Majma` al-zawa'id (10:74) said that its narrators are all trustworthy (thiqat), while Suyuti declared it hasan in his Jami` al-saghir (#7701).
Allah SWT placed His remembrance above prayer in value by making prayer the means and remembrance the goal. He said: "Lo! Worship guards one from lewdness and iniquity, but verily, remembrance of Allah is greater/more important." (29:45) "He is successful who purifies himself, and remembers the name of his Lord, and so prays." (87:14-15) "So establish prayer for My remembrance." (20:14)
Ibn Hajar in his Fath al-bari (1989 ed. 11:251) relates Qadi Abu Bakr Ibn al-`Arabi's explanation that there is no good deed except with dhikr as a precondition for its validity, and whoever does not remember Allah in his heart at the time of his sadaqa or fasting, for example, then his deed is incomplete: therefore dhikr is the best of deeds because of this.
Dhikr is, therefore, something of tremendous importance. Abu Hurayra RA said that Rasulullah SAW said, Peace be upon him: "The earth and everything in it is cursed, except for dhikr and what attends dhikr, and a teacher (of dhikr) and a student (of dhikr)." Narrated by Tirmidhi. By the words "the world and everything in it" is meant here all that claims status or existence apart from Allah SWT instead of in Him. In fact, all creation does dhikr because Allah said that all creation does praise to Him constantly, and tasbih is a kind of dhikr. Allah said of the Prophet Yunus, when the whale swallowed him: "Had he not been one of My glorifiers (musabbihin) , he would have remained inside the whale's stomach until Judgment Day." (37:143-144)
The one who engages in dhikr has the highest rank of all before Allah SWT . The people who call on Allah without distraction have been mentioned in Qur'an, as well as the effect that calling has on their heart: "In houses which Allah has allowed to be raised to honour and for His Name to be remembered in them; He is glorified there day and night by men whom neither trade nor sale can divert from the remembrance of Allah SWT " (24:36-37).”Those who believe and their hearts find satisfaction in the remembrance of Allah: By remembering Allah, truly satisfaction comes to the heart" (13:28).
During the night of Isra' and Mi`raj, the Prophet was taken up to a point where he heard the screeching of the Pens (writing the divine Decree). He saw a man who had disappeared into the light of the Throne. He said: "Who is this? Is this an angel?" It was said to him, no. He said: "Is it a Prophet?" Again the answer was no. He said: "Who is it then?" The answer was: "This is a man, whose tongue was moist with Allah's remembrance in the world, and his heart was attached to the masjid, and he never incurred the curse of his father and mother."
A man came to Rasulullah SAW and said, "O Rasulallah, the laws and conditions of Islam have become too many for me. Tell me something that I can always keep (i.e. in particular, as opposed to the many rules and conditions that must be kept in general)." By reading that the man said there were too many conditions to keep, one must understand that he was unsure that he could keep them all. He wanted something that he would be sure to keep always. The Prophet said: "(I am advising you in one thing :) Keep your tongue always moist with dhikrullah ."
It is well-known in Islam that the best work in the path of Allah is jihad. Yet Rasulullah SAW placed dhikr even above jihad in the following authentic hadiths:
Abu al-Darda' narrates: The Prophet once asked his companions: "Shall I tell you about the best of all deeds, the best act of piety in the eyes of your Lord, which will elevate your status in the Hereafter, and carries more virtue than the spending of gold and silver in the service of Allah SWT or taking part in jihad and slaying or being slain in the path of Allah? The dhikr of Allah." Related in the Malik's Muwatta' , the Musnad of Ahmad, the Sunan of Tirmidhi, Ibn Majah, and the Mustadrak of Hakim. Al-Bayhaqi, Hakim and others declared it sahih.
Abu Sa`id RA narrates: Rasulullah SAW was asked, "Which of the servants of Allah is best in rank before Allah on the Day of resurrection?" He said: "The ones who remember him much." I said: "O Messenger of Allah, what about the fighter in the way of Allah?" He answered: "Even if he strikes the unbelievers and mushrikin with his sword until it broke, and becomes red with their blood, truly those who do dhikr are better than him in rank." Related in Ahmad, Tirmidhi, and Bayhaqi.