Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 526
Narrated Ibn Abbas:
Allah's Apostle used to say at the time of difficulty, "None has the right to be worshipped but Allah, the Majestic, the Most Forbearing. None has the right to be worshipped but Allah, the Lord of the Tremendous Throne. None has the right to be worshipped but Allah, the Lord of the Heavens and the Lord of the Honourable Throne. (See Hadith No. 357, Vol. 8)