The Prophet ﷺ heard a man saying, "Allah, I ask You by the fact that You are Allah, the One, the Eternal, who did not beget and was not begotten, and to whom none is equal."The Messenger of Allah ﷺ said, "He has asked Allah by His Greatest Name, the name by which when He is asked, He gives, and when He is called upon, He answers."
حدثنا علي بن محمد حدثنا وكيع عن مالك بن مغول أنه سمعه من
سمع النبي ﷺ رجلا يقول اللهم إني أسألك بأنك أنت الله الأحد الصمد الذي لم يلد ولم يولد ولم يكن له كفوا أحد فقال رسول الله ﷺ لقد سأل الله باسمه الأعظم الذي إذا سئل به أعطى وإذا دعي به أجاب
[Its chain of transmission is sahih] Abu Dawud narrated it in the chapter on Prayer, section on supplication, hadith no. 1493, from the hadith of Malik bin Mughul, with this same wording. Tirmidhi, hadith no. 3475, said, "Hasan gharib." Ibn Hibban graded it sahih, hadith no. 2383, as did Hakim, who said it met the standard of the two Shaykhs, 1/504, and Dhahabi concurred with him.