The greatest name of Allah
The Prophet (sal Allahu alaihi wa sallam) said: “The greatest name of Allah appears in three surahs of the Qur’an: in al-Baqarah, Aal ‘Imraan and Ta-Ha.”
[Sunan Ibn Majaah Classed as Hasan by al-Albaani]
Shaykh al-Albaani (may Allah have mercy on him) said regarding the above Hadith:
With regard to the words of al-Qaasim ibn ‘Abd al-Rahman (the one who narrated it from Abu Umaamah) that the greatest name is found in the verse (interpretation of the meaning): “And (all) faces shall be humbled before (Allah), Al-Hayyul-Qayyum (the Ever Living, the One Who sustains and protects all that exists)” [Ta-Ha 20:111] in Surat Ta-Ha, I could not find anything to support it. It is more likely in my view that it is in the verse at the beginning of the surah: “Verily, I am Allah! Laa ilaaha illa Ana (none has the right to be worshipped but I)” [Ta-Ha 20:14], and that is in accordance with some sahih ahadith. [See: al-Fath (11/225) and Saheeh Abi Dawood (1341)]
And Allah knows best!