Hadith 580B2

قَالَ يَحْيَى : وَسَمِعْتُ مَالِكًا يَقُولُ : إِذَا صَامَ النَّاسُ يَوْمَ الْفِطْرِ ، وَهُمْ يَظُنُّونَ أَنَّهُ مِنْ رَمَضَانَ ، فَجَاءَهُمْ ثَبْتٌ أَنَّ هِلَالَ رَمَضَانَ قَدْ رُئِيَ قَبْلَ أَنْ يَصُومُوا بِيَوْمٍ ، وَأَنَّ يَوْمَهُمْ ذَلِكَ أَحَدٌ وَثَلَاثُونَ ، فَإِنَّهُمْ يُفْطِرُونَ فِي ذَلِكَ الْيَوْمِ أَيَّةَ سَاعَةٍ جَاءَهُمُ الْخَبَرُ غَيْرَ أَنَّهُمْ لَا يُصَلُّونَ صَلَاةَ الْعِيدِ إِنْ كَانَ ذَلِكَ جَاءَهُمْ بَعْدَ زَوَالِ الشَّمْسِ
Imam Malik, may Allah have mercy on him, said: If people fasted on the day of Eid thinking that it was a day of Ramadan, and then a trustworthy person came and said that the moon had been sighted a day before you began fasting and that this day is the thirty-first, then they should break their fast as soon as they receive this news. However, if the time of decline (zawal) has passed, then they should not perform the Eid prayer.
Hadith Reference موطا امام مالك رواية يحييٰ / كتاب الصيام / 580B2
Hadith Takhrij «شركة الحروف نمبر: 586، فواد عبدالباقي نمبر: 18 - كِتَابُ الصِّيَامِ-ح: 4»