The Book of Manners and Etiquette
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَابْنُ أَبِي عُمَرَ، قَالاَ حَدَّثَنَا سُفْيَانُ، عَنْ يَزِيدَ بْنِ خُصَيْفَةَ، بِهَذَا الإِسْنَادِ . وَزَادَ ابْنُ أَبِي عُمَرَ فِي حَدِيثِهِ قَالَ أَبُو سَعِيدٍ فَقُمْتُ مَعَهُ فَذَهَبْتُ إِلَى عُمَرَ فَشَهِدْتُ .This hadith has been narrated on the authority of Yazid b. Khusaifa with the same chain of transmitters but with this addition:Abu Sa'id said: So I stood up, and went to 'Umar and gave witness (to what Abu Musa had said)
From Sahih Muslim, whose reports the scholars accept as authentic.