Sunan Ibn Majah, Volume 2, Book 6, Hadith 1557 (DarusSalam) ⓘ

It was narrated that Anas bin Malik said: “When the Prophet died, there was a man in Al-Madinah who used to make a niche in the grave and another who used to dig graves without a niche. They said: ‘Let us pray Istikharah to our Lord and call for them both, and whichever of them comes first, we will let him do it.’ So they were both sent for, and the one who used to make the niche-grave came first, so they made a niche-grave for the Prophet.”

حَدَّثَنَا مَحْمُودُ بْنُ غَيْلاَنَ، حَدَّثَنَا هَاشِمُ بْنُ الْقَاسِمِ، حَدَّثَنَا مُبَارَكُ بْنُ فَضَالَةَ، حَدَّثَنِي حُمَيْدٌ الطَّوِيلُ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ لَمَّا تُوُفِّيَ النَّبِيُّ ـ صلى الله عليه وسلم ـ كَانَ بِالْمَدِينَةِ رَجُلٌ يَلْحَدُ وَآخَرُ يَضْرَحُ فَقَالُوا نَسْتَخِيرُ رَبَّنَا وَنَبْعَثُ إِلَيْهِمَا فَأَيُّهُمَا سَبَقَ تَرَكْنَاهُ ‏.‏ فَأُرْسِلَ إِلَيْهِمَا فَسَبَقَ صَاحِبُ اللَّحْدِ فَلَحَدُوا لِلنَّبِيِّ ـ صلى الله عليه وسلم ـ ‏.‏