Bulugh al-Maram, Book 3, Hadith 606 (English) ⓘ

‘Uthman Ibn ‘Affan (RAA) narrated, ‘Whenever the Messenger of Allah finished the burial of the dead, he would stand by the grave and say, “Seek forgiveness for your brother and pray for him to be steadfast, because he is now being questioned.” Related by Abu Dawud. Al-Hakim graded it as Sahih.

وَعَنْ عُثْمَانَ ‏- رضى الله عنه ‏- قَالَ: { كَانَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-إِذَا فَرَغَ مِنْ دَفْنِ الْمَيِّتِ وَقَفَ عَلَيْهِ وَقَالَ: "اِسْتَغْفِرُوا لِأَخِيكُمْ وَسَلُوا لَهُ التَّثْبِيتَ, فَإِنَّهُ الْآنَ يُسْأَلُ" } رَوَاهُ أَبُو دَاوُدَ, وَصَحَّحَهُ الْحَاكِم ُ 1‏.‏ ‏1 ‏- صحيح.‏ رواه أبو داود (3221)‏، والحاكم (1/370)‏ وفي "أ": "واسألوا".‏