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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
ahmad:11242 – Ibrāhīm b. Isḥāq > Ibn Mubārak > Saʿīd b. ʿAbd al-ʿAzīz > ʿAṭiyyah b. Qays > Qazaʿah > Abū Saʿīd al-Khudrī

"During the year of the conquest, when the Prophet ﷺ reached Marr Zahran, he told us that we would meet the enemy. So he ordered us to break the fast, and we [all] broke our fast." (Using translation from Tirmidhī 1684)   

أحمد:١١٢٤٢ – حَدَّثَنَا إِبْرَاهِيمُ بْنُ إِسْحَاقَ حَدَّثَنَا ابْنُ مُبَارَكٍ عَنْ سَعِيدِ بْنِ عَبْدِ الْعَزِيزِ عَنْ عَطِيَّةَ بْنِ قَيْسٍ عَنْ قَزَعَةَ عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ

لَمَّا بَلَغَ رَسُولُ اللهِ ﷺ عَامَ الْفَتْحِ مَرَّ الظَّهْرَانِ آذَنَنَا بِلِقَاءِ الْعَدُوِّ فَأَمَرَنَا بِالْفِطْرِ فَأَفْطَرْنَا أَجْمَعُونَ  

See similar narrations below:

Collected by Tirmidhī
tirmidhi:1684 – Aḥmad b. Muḥammad b. Mūsá > ʿAbdullāh b. al-Mubārak > Saʿīd b. ʿAbd al-ʿAzīz > ʿAṭiyyah b. Qays > Qazaʿah > Abū Saʿīd al-Khudrī

"During the year of the conquest, when the Prophet ﷺ reached Marr Zahran, he told us that we would meet the enemy. So he ordered us to break the fast, and we [all] broke our fast."  

[Abu 'Eisa said:] This Hadith is Hasan Sahih, and there is something on this topic from Ibn 'Umar.
الترمذي:١٦٨٤ – حَدَّثَنَا أَحْمَدُ بْنُ مُحَمَّدِ بْنِ مُوسَى أَنْبَأَنَا عَبْدُ اللَّهِ بْنُ الْمُبَارَكِ أَنْبَأَنَا سَعِيدُ بْنُ عَبْدِ الْعَزِيزِ عَنْ عَطِيَّةَ بْنِ قَيْسٍ عَنْ قَزَعَةَ عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ

لَمَّا بَلَغَ النَّبِيُّ ﷺ عَامَ الْفَتْحِ مَرَّ الظَّهْرَانِ فَآذَنَنَا بِلِقَاءِ الْعَدُوِّ فَأَمَرَنَا بِالْفِطْرِ فَأَفْطَرْنَا أَجْمَعُونَ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ وَفِي الْبَابِ عَنْ عُمَرَ