Al-Ism al-A'zam

' (الاسم الأعظم), literally "the Greatest Name",   also known as ' (اسم الله الأکبر),  refers in Islam to the greatest name of Allah,  known only to the prophets.

Significance
According to some Islamic hadiths, whoever calls to God using, his or her prayer (du'a) will be granted.

In Shi'a Islam, is believed to have a powerful effect in the act of blessing.