وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّهُ قَالَ كَانَ بِالْمَدِينَةِ رَجُلاَنِ أَحَدُهُمَا يَلْحَدُ وَالآخَرُ لاَ يَلْحَدُ فَقَالُوا أَيُّهُمَا جَاءَ أَوَّلُ عَمِلَ عَمَلَهُ ‏.‏ فَجَاءَ الَّذِي يَلْحَدُ فَلَحَدَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم ‏.‏

Yahya related to me from Malik from Hisham ibn Urwa that hisfather said, "There were two men in Madina, one of whom dug graveswith a niche in the side wall for the body, and the other who did not,and they said, 'Whichever one comes first can do the job,' and the onewho dug graves with a niche came first and dug the Messenger ofAllah's grave, may Allah bless him and grant him peace." Translation Not Available

Book Ref: Muwatta Imam Malik Book 16 Hadith 550
Web Ref:  Muwatta Imam Malik Book 16 Hadith 28