Sahih Muslim
The Book Pertaining to Paradise, Its Description, Its Bounties and Its Intimates (Kitab Al-Jannat wa Sifat Naimiha wa Ahliha)
Book Number: 040 / Hadith Number: 6865
Al-Bara' b. 'Azib reported Allah's Apostle (may peace be upon him) as saying: This verse:" Allah grants steadfastness to those who believe with firm word," was rereaied in connection with the torment of the grave. It would be said to him: Who is your Lord? And he would say: Allah is my Lord and Muhammad is my Apostle (may peace be upon him), and that is (what is implied) by the words of Allah, the Exalted:" Allah keeps steadfast those who believe with firm word in this world and in the Hereafter."