Language:
كتاب الصوم
30  
Fasting
(46)
Chapter: If somebody breaks the Saum thinking that the sun has set
(46)
باب إِذَا أَفْطَرَ فِي رَمَضَانَ ثُمَّ طَلَعَتِ الشَّمْسُ
Sahih al-Bukhari 1959

Narrated Abu Usama from Hisham bin 'Urwa from Fatima:

Asma bint Abi Bakr said, "We broke our fast during the lifetime of the Prophet (ﷺ) on a cloudy day and then the sun appeared." Hisham was asked, "Were they ordered to fast in lieu of that day?" He replied, "It had to be made up for." Ma`mar said, "I heard Hisham saying, "I don't know whether they fasted in lieu of that day or not."

حَدَّثَنِي عَبْدُ اللَّهِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ فَاطِمَةَ، عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ ـ رضى الله عنهما ـ قَالَتْ أَفْطَرْنَا عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم يَوْمَ غَيْمٍ، ثُمَّ طَلَعَتِ الشَّمْسُ‏.‏ قِيلَ لِهِشَامٍ فَأُمِرُوا بِالْقَضَاءِ قَالَ بُدٌّ مِنْ قَضَاءٍ‏.‏ وَقَالَ مَعْمَرٌ سَمِعْتُ هِشَامًا لاَ أَدْرِي أَقْضَوْا أَمْ لاَ‏.‏
Reference : Sahih al-Bukhari 1959
In-book reference : Book 30, Hadith 66
USC-MSA web (English) reference : Vol. 3, Book 31, Hadith 180
  (deprecated numbering scheme)