عن جابر رضي الله عنه قال: سمعت رسول الله صلى الله عليه وسلم يقول: «أفضل الذِّكر: لا إله إلا الله». [حسن] - [رواه الترمذي والنسائي في الكبرى وابن ماجه] المزيــد ...
Jābir (may Allah be pleased with him) narrated that he heard the Messenger of Allah (may Allah's peace and blessings be upon him) say: "The best Dhikr is: There is no god but Allah." Hasan/Sound. - [Ibn Maajah]
In this Hadīth, the Prophet (may Allah's peace and blessings be upon him) informs us that the best words of Dhikr is to say: There is no god but Allah.
In another Hadīth, he said:"The best of what I and the prophets before me said is: There is no god but Allah, alone who has no partner."
There is no doubt that this is a great statement: the heavens and the earth were established by it and all creation was created for it. For this statement Allah, the Almighty, sent His messengers, revealed His books, and legislated His laws. For this statement the scales of justice were instituted, the records of deeds were kept, the market for Paradise and Hell was set up (an idiom of gaining or losing by good or bad deeds that lead to Paradise or Hellfire).
Its meaning is: There is no god but Allah. Its conditions are seven: knowledge, certainty, acceptance, obedience, truthfulness, sincerity, and love. All past and future nations will be questioned about it. On the Day of Judgment when each and every person will stand before Allah, they will not be able to move from their places until they are asked what they worshiped and what was their response to the messengers of Allah (i.e. the meaning and significance of this statement).
The answer to the first question (concerning Allah) is by fulfilling the statement "There is no god but Allah" in knowledge, belief, and action. The answer to the second question (about the Prophet) is by fulfilling the statement "Muhammad is the Messenger of Allah" in knowledge, belief, action, and obedience.
The Prophet (may Allah's peace and blessings be upon him) said: "Islam is based on five pillars: Testifying that there is no god but Allah and that Muhammad is the Messenger of Allah..."
The word of monotheism is the best speech, for it affirms the oneness of Allah and denies the existence of partners with Him. It is the best phrase uttered by the prophets, who were sent for its sake, fought under its banner, and were martyred in its cause. It is the key to entering Paradise and salvation from Hellfire.