When the Messenger of Allah ﷺ reached Marr al-Zahran during the year of the Conquest, he informed us that we would be meeting the enemy and ordered us to break our fast, so we all broke our fast.
حدثنا إبراهيم بن إسحاق حدثنا ابن مبارك عن سعيد بن عبد العزيز عن عطية بن قيس عن قزعة
لما بلغ رسول الله ﷺ عام الفتح مر الظهران آذننا بلقاء العدو فأمرنا بالفطر فأفطرنا أجمعون
Its isnad is sahih. Abu Salama is Salama bin Mansur Khuzai, who is trustworthy. Ibn Mubarak is Abdullah. Saeed bin Abdul-Aziz is trustworthy, and likewise Atiya bin Qays. Qazaa is Ibn Yahya Basri, who is also trustworthy.The hadith, with similar wording, appears in Bukhari 3/180 no. 1944, and Muslim no. 1113.