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He also said that when the Prophet (ﷺ) finished the burial of the dead he stood over it and said, “Ask forgiveness for your brother, then ask that he may be strengthened, for he is now being questioned." Abu Dawud transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَن عُثْمَان رَضِيَ اللَّهُ عَنْهُ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا فَرَغَ مِنْ دَفْنِ الْمَيِّتِ وَقَفَ عَلَيْهِ فَقَالَ: «اسْتَغْفِرُوا لِأَخِيكُمْ ثُمَّ سَلُوا لَهُ بِالتَّثْبِيتِ فَإِنَّهُ الْآنَ يُسْأَلُ» . رَوَاهُ أَبُو دَاوُد
sunnah.com