O Allah, so-and-so the son of so-and-so is under Your protection and mercy. So, protect him from the trial of the grave and the torture of Hellfire. You are worthy of fulfilling promises and worthy of praise. O Allah, forgive him and have mercy upon him, as You are the Most Forgiving and the Most Merciful
Authentic hadithعن واثلة بن الأسقع رضي الله عنه مرفوعاً: « صلى بنا رسول الله صلى الله عليه وسلم على رجل من المسلمين، فسمعته يقول: «اللهم إن فلان ابن فلان في ذمتك وحبل جِوَارِكَ، فَقِهِ فِتْنَةَ القبر، وعذاب النار، وأنت أهل الوفاء والحمد؛ اللهم فاغفر له وارحمه، إنك أنت الغفور الرحيم».
Wāthilah ibn al-Asqa‘ (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) led us in prayer over a dead man from among the Muslims. I heard him say: "O Allah, so-and-so the son of so-and-so is under Your protection and mercy. So, protect him from the trial of the grave and the torture of Hellfire. You are worthy of fulfilling promises and worthy of praise. O Allah, forgive him and have mercy upon him, as You are the Most Forgiving and the Most Merciful."
Explanation
The Prophet (may Allah's peace and blessings be upon him) performed the funeral prayer over a deceased from among the Muslims. Then, he said what means: O Allah, so-and-so the son of so-and-so is under Your safety, protection, and seeking Your forgiveness. Make him firm during the questioning and examination in the grave and save him from the torment of the Fire. Indeed, You do not break Your promise and You are worthy of truth. O Allah, forgive him and be merciful to him. You are Oft-Forgiving of sins and Most Merciful by accepting acts of obedience and multiplying rewards.
Source · Narrated by Ibn Majah - Narrated by Abu Daoud - Narrated by Ahmad
From the Hadith Encyclopedia (hadeethenc.com).