AL-ISMU ‘L-A’ZAM الاسم الاعظم
The exalted name of God, which is generally believed to be known only to the Prophets. Muhammad is related to have said that it occurs in either the Suratu ‘l-Baqarah, ii, 256: “God (Allah) there is no God but He (Hu) the Living (al-Haiy), the Self-subsistent (al-Qaiyum)”; or in the Suratu ‘Ali ‘Imran, iii 1, which contains the same words; or in the Suratu Ta Ha, xx 110: “Faces shall be humbled before the Living (al-Haiy) and the Self-subsistent (al-Qaiyum).”
It is therefore generally held to be either Allah, or Hu, or al-Haiy, or al-Qaiyum.
It is very probable that the mysterious title of the Divine Being refers to the great name of Jehovah, the superstitions reverence for which on the part of the Jews must have been well known to Muhammad.
Based on Hughes, Dictionary of Islam