حَدَّثَنَا أَبُو الْوَلِيدِ الطَّيَالِسِيُّ، حَدَّثَنَا شُعْبَةُ، عَنْ عَلْقَمَةَ بْنِ مَرْثَدٍ، عَنْ سَعْدِ بْنِ عُبَيْدَةَ، عَنِ الْبَرَاءِ بْنِ عَازِبٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏:‏ ‏"‏ إِنَّ الْمُسْلِمَ إِذَا سُئِلَ فِي الْقَبْرِ فَشَهِدَ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ صلى الله عليه وسلم فَذَلِكَ قَوْلُ اللَّهِ عَزَّ وَجَلَّ ‏{‏ يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ ‏}‏ ‏.‏

Al-Bara’ b. ‘Azib reported the Messenger of Allah(PBUH) as saying: When a Muslim is questioned in the grave he testifies that there is no god but Allah and that Muhammad is Allah’s Apostle. That is verified by Allah’s words: “Allah establishes those who believe with the word that stands firm.” Translation Not Available

Book Ref: Sunan Abi Dawud Book 42 Hadith 4750
Web Ref:  Sunan Abi Dawud Book 41 Hadith 4732