بُلُوغُ الْمَرَامِ
Bulugh al-Maram 486
The Book of Prayer
وَعَنْ أَبِي عُمَيْرِ بْنِ أَنَسٍ, عَنْ عُمُومَةٍ لَهُ مِنَ اَلصَّحَابَةِ, { أَنَّ رَكْبًا جَاءُوا, فَشَهِدُوا أَنَّهُمْ رَأَوُا الْهِلَالَ بِالْأَمْسِ, فَأَمَرَهُمْ اَلنَّبِيُّ - صلى الله عليه وسلم -أَنْ يُفْطِرُوا, وَإِذَا أَصْبَحُوا يَغْدُوا إِلَى مُصَلَّاهُمْ } رَوَاهُ أَحْمَدُ, وَأَبُو دَاوُدَ -وَهَذَا لَفْظُهُ- وَإِسْنَادُهُ صَحِيحٌ [1] .
Narrated Abu 'Umair bin Anas bin Malik (RA) on the authority of some of his paternal uncles who were among the Companions, that some riders came and testified that they had seen the new moon the previous day. The Prophet (ﷺ) therefore commanded the people to break the fast and go out to their place of prayer in the morning. [Reported by Ahmad and Abu Dawud. This is Abu Dawud's wording and its Isnad is Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 411