The Book of Jihad and Expeditions
حَدَّثَنَا مُحَمَّدُ بْنُ عَبَّادٍ، حَدَّثَنَا حَاتِمٌ، - يَعْنِي ابْنَ إِسْمَاعِيلَ - عَنْ يَزِيدَ، - وَهُوَ ابْنُ أَبِي عُبَيْدٍ قَالَ سَمِعْتُ سَلَمَةَ، يَقُولُ غَزَوْتُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم سَبْعَ غَزَوَاتٍ وَخَرَجْتُ فِيمَا يَبْعَثُ مِنَ الْبُعُوثِ تِسْعَ غَزَوَاتٍ مَرَّةً عَلَيْنَا أَبُو بَكْرٍ وَمَرَّةً عَلَيْنَا أُسَامَةُ بْنُ زَيْدٍ .It has been narrated on the authority of Salama who said:I joined seven military expeditions led by the Messenger of Allah himself (ﷺ), and nine expeditions which he sent out once under Abu Bakr and once under Usama b. Zaid
From Sahih Muslim, whose reports the scholars accept as authentic.