Hadith: O Allah, I ask You by virtue of my testimony that You are Allah; there is no God but You, the One, the Eternal Refuge, Who did not beget, and was not begotten, and to Whom no one is equal

عن بريدة رضي الله عنه قال: سمع النبي صلى الله عليه وسلم رجلاً يقول: اللهم إني أسألك بأني أشهد أنك أنت الله لا إله إلا أنت، الأحد الصمد، الذي لم يلد، ولم يولد، ولم يكن له كفوًا أحد. فقال: «لقد سأل الله باسمه الذي إذا سُئِلَ به أعطى، وإذا دُعِيَ به أجاب»
[صحيح] - [رواه أبو داود والترمذي والنسائي وابن ماجه]

Buraydah (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) once heard a man saying: "O Allah, I ask You by virtue of my testimony that You are Allah, there is no God but You, the One, the Eternal Refuge, Who did not beget, and was not begotten, and to Whom no one is equal." Thereupon, he: "Verily, he has asked Allah by His Name by which He gives when asked, and by which He answers when supplicated."
Sahih/Authentic. - [Ibn Maajah]

Explanation

This great supplication which the Prophet (may Allah's peace and blessings be upon him) heard a Bedouin supplicate and implore Allah with, includes the Greatest Name of Allah. It indicates that Allah is One, Unique, the Eternal Refuge, upon Whom all people depend in fulfilling their needs. He is The One Who does not beget, because He has no equivalent and is Free of need to anyone. He was not begotten, and there is none like Him in terms of His Essence, Attributes and Actions. These great meanings are the foundation of Islamic monotheism, and are all combined in this great supplication. This is what makes it the greatest type of supplication. There is no servant who supplicates Allah with this supplication, except that Allah will give him what he asks for.