I said to Sha'bi: Who narrated it to you? He said: An authentic one, 'Abdullah b. 'Abbas. This is the word of a hasan hadith. In the narration of Ibn Numair (the words are): The Messenger of Allah ﷺ went to the grave which had been newly prepared and prayed over it, and they also prayed who were behind him and he recited four takbirs. I said to 'Amir: Who narrated it to you? He said: An authentic one who saw him, i e. Ibn 'Abbas.  

أَنَّ رَسُولَ اللَّهِ ﷺ صَلَّى عَلَى قَبْرٍ بَعْدَ مَا دُفِنَ فَكَبَّرَ عَلَيْهِ أَرْبَعًا قَالَ الشَّيْبَانِيُّ فَقُلْتُ لِلشَّعْبِيِّ مَنْ حَدَّثَكَ بِهَذَا قَالَ الثِّقَةُ عَبْدُ اللَّهِ بْنُ عَبَّاسٍ هَذَا لَفْظُ حَدِيثِ حَسَنٍ وَفِي رِوَايَةِ ابْنِ نُمَيْرٍ قَالَ انْتَهَى رَسُولُ اللَّهِ ﷺ إِلَى قَبْرٍ رَطْبٍ فَصَلَّى عَلَيْهِ وَصَفُّوا خَلْفَهُ وَكَبَّرَ أَرْبَعًا قُلْتُ لِعَامِرٍ مَنْ حَدَّثَكَ قَالَ الثِّقَةُ مَنْ شَهِدَهُ ابْنُ عَبَّاسٍ