Sunan Ibn Majah, Chapter: The Chapters on Supplication

that his father said: "The Prophet (saw) heard a man say: 'Allahumma! Inni as'aluka bi-annaka Antallahul-Ahadus-Samad, alladhi lam yalid wa lam yuwlud, wa lam yakun lahu kufuwan ahad (O Allah! I ask You by virtue of Your being Allah, the One, the Self-Sufficient Master, Who begets not nor was begotten, and there is none co-equal or comparable to Him).' The Messenger of Allah (saw) said: 'He has asked Allah by His Greatest Name, which if He is asked thereby He gives, and if He is called upon thereby He answers.'"