Hadith Research Libraryمكتبة الحديث والرجال
Mishkat al-Masabih, 133
graded· Zubair `Aliza'i

Hadith text · Matn

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

English translation

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.

References1 variant
In-Book Reference
Book 1, Hadith 126