What is the Greatest Name of God?
There are statements mentioned in the hadith that definitively answer this question.
It was narrated in the hadith of Buraidah when the Prophet Muhammad (peace be upon him) heard a man praying, saying,
“O Allah, I ask You by the fact that I bear witness that You are Allah, there is no god but You, the One, the Eternal Refuge, who neither begets nor is born, and there is none comparable to Him.”
The Prophet (peace be upon him)
then said, “By the One in Whose hand is my soul, he has asked Allah by His Greatest Name, which, when He is called upon by it, He responds, and when asked by it, He gives.”
In another hadith narrated by Anas (may Allah be pleased with him), he was sitting with the Prophet (peace be upon him) and a man was praying, saying,
“O Allah, I ask You because all praise is due to You; there is no god but You, the Most Generous, the Originator of the heavens and the earth, O Lord of Majesty and Honour, O Ever-Living, O Sustainer.”
The Prophet (peace be upon him) then said, “He has called upon Allah by His Greatest Name, which, when He is called upon by it, He responds, and when asked by it, He gives.”
Sheikh Ibn Uthaymeen was certain that the Greatest Name of Allah is “Al-Hayy Al-Qayyum” (The Ever-Living, the Sustainer), which is also the opinion of Imam Ibn Taymiyyah and Ibn Al-Qayyim, may Allah have mercy on them all.
In the hadith of Asma bint Yazid, the Prophet (peace be upon him) said, “The Greatest Name of God is in these two verses:
Ayat al-Kursi (Allah! There is no god but He, the Ever-Living, the Sustainer), and the verse from Al-Imran (Alif-Lam-Mim. Allah! There is no god but He, the Ever-Living, the Sustainer).”
It is clear from these hadiths that the Greatest Name of Allah could be “Al-Hayy Al-Qayyum” or
“O Allah, I ask You because all praise is due to You; there is no god but You, the Most Generous, the Originator of the heavens and the earth, O Lord of Majesty and Honour, O Ever-Living, O Sustainer,”
as mentioned in the hadith of Buraidah. Some scholars also believe that the Greatest Name of Allah is found in the declaration of monotheism (Tawhid), as it is the common factor in the aforementioned hadiths. Therefore, when a Muslim calls upon Allah with these names together, he is invoking the Greatest Name of Allah.