The Book of Jihad and Expeditions
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ - وَاللَّفْظُ لاِبْنِ الْمُثَنَّى - قَالاَ حَدَّثَنَا مُحَمَّدُ، بْنُ جَعْفَرٍ حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي إِسْحَاقَ، أَنَّ عَبْدَ اللَّهِ بْنَ يَزِيدَ، خَرَجَ يَسْتَسْقِي بِالنَّاسِ فَصَلَّى رَكْعَتَيْنِ ثُمَّ اسْتَسْقَى قَالَ فَلَقِيتُ يَوْمَئِذٍ زَيْدَ بْنَ أَرْقَمَ - وَقَالَ - لَيْسَ بَيْنِي وَبَيْنَهُ غَيْرُ رَجُلٍ أَوْ بَيْنِي وَبَيْنَهُ رَجُلٌ - قَالَ - فَقُلْتُ لَهُ كَمْ غَزَا رَسُولُ اللَّهِ صلى الله عليه وسلم قَالَ تِسْعَ عَشْرَةَ فَقُلْتُ كَمْ غَزَوْتَ أَنْتَ مَعَهُ قَالَ سَبْعَ عَشْرَةَ غَزْوَةً - قَالَ - فَقُلْتُ فَمَا أَوَّلُ غَزْوَةٍ غَزَاهَا قَالَ ذَاتُ الْعُسَيْرِ أَوِ الْعُشَيْرِ .It has been narrated on the authority of Abu Ishaq that 'Abdullah b. Yazid went (out of the city) with people for offering" Istisqa" ' prayer (for rainfall). He offered two rak'ahs. Then he prayed for rain. That day I met Zaid b. Arqam. There was only one man between me and him (at that time). I asked him:How many military expeditions did the Messenger of Allah (ﷺ) undertake? He said: Nineteen expeditions. I asked him: On how many expeditions did you accompany him? He said: On seventeen expeditions. I asked: Which was the first expedition he led? He answered: Dhat-ul-, Usair or 'Ushair
From Sahih Muslim, whose reports the scholars accept as authentic.