Dr. Marawan Shahin, Professor of Hadith and its Sciences, Faculty of Usul Ad-Din (Theology), Al-Azhar Univ. states: “Recitng ‘la ilaha illa Allah’ is the best of dhikr (remembrance of Allah). The Prophet (peace and blessings be upon him) is reported to have said, “The best of what I as well as all prophets before me said is: There is no god but Allah, with no partner or associate; His is the Dominion, to Him be all praise, and He is able to do all things”.
The Prophet (peace and blessings be upon him) is also reported to have said, “Whoever says, ‘Laa ilaha ill Allaah wahdahu laa shareeka lah, lahu al-mulk wa lahu al-hamd wa huwa `ala kulli shay’in qadeer (there is no god but Allah, with no partner or associate; His is the Dominion, to Him be all praise, and He is able to do all things)” one hundred times in a day, it will be as if he freed ten slaves, and one hundred hasanah (good deeds) will be recorded for him, and one hundred bad deeds will be erased from him, and it will be a protection for him against the Shaytan all that day until evening comes. No one can do anything better than that except one who does more.” (Reported by Al-Bukhari and Muslim)