Sahih Muslim 1814
Sahih Muslim · Book 32: The Book of Jihad and Expeditions · The number of campaigns of the Prophet (saws)
وَحَدَّثَنِي أَحْمَدُ بْنُ حَنْبَلٍ ، حَدَّثَنَا مُعْتَمِرُ بْنُ سُلَيْمَانَ ، عَنْ كَهْمَسٍ ، عَنِ ابْنِ بُرَيْدَةَ ، عَنْ أَبِيهِ ، أَنَّهُ قَالَ غَزَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم سِتَّ عَشْرَةَ غَزْوَةً .
It has been narrated by Buraida who heard it from his father that he joined the Messenger of Allah (ﷺ) in sixteen military campaigns