[Machine] I saw the Prophet ﷺ when he buried Uthman ibn Mazh'un. He prayed and prayed four takbeers and then made three handfuls of soil from the earth while standing on the grave. The chain of narration is weak, except that there is a witness from Ja'far ibn Muhammad narrating from his father, who narrates from the Prophet ﷺ in a mursal (incomplete chain) narration. It is also narrated from Abu Huraira, elevated. And Allah knows best.  

رَأَيْتُ النَّبِيَّ ﷺ حِينَ دَفَنَ عُثْمَانَ بْنَ مَظْعُونٍ ؓ فَصَلَّى عَلَيْهِ وَكَبَّرَ عَلَيْهِ أَرْبَعًا وَحَثَا بِيَدَيْهِ ثَلَاثَ حَثَيَاتٍ مِنَ التُّرَابِ وَهُوَ قَائِمٌ عَلَى الْقَبْرِ إِسْنَادُهُ ضَعِيفٌ إِلَّا أَنَّ لَهُ شَاهِدًا مِنْ جِهَةِ جَعْفَرِ بْنِ مُحَمَّدٍ عَنْ أَبِيهِ عَنِ النَّبِيِّ ﷺ مُرْسَلًا وَيُرْوَى عَنْ أَبِي هُرَيْرَةَ ؓ مَرْفُوعًا وَاللهُ أَعْلَمُ