حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَخِيهِ، خَالِدِ بْنِ أَسْلَمَ أَنَّ عُمَرَ بْنَ الْخَطَّابِ، أَفْطَرَ ذَاتَ يَوْمٍ فِي رَمَضَانَ فِي يَوْمٍ ذِي غَيْمٍ وَرَأَى أَنَّهُ قَدْ أَمْسَى وَغَابَتِ الشَّمْسُ . فَجَاءَهُ رَجُلٌ فَقَالَ يَا أَمِيرَ الْمُؤْمِنِينَ طَلَعَتِ الشَّمْسُ . فَقَالَ عُمَرُ الْخَطْبُ يَسِيرٌ وَقَدِ اجْتَهَدْنَا . قَالَ مَالِكٌ يُرِيدُ بِقَوْلِهِ الْخَطْبُ يَسِيرٌ الْقَضَاءَ فِيمَا نُرَى - وَاللَّهُ أَعْلَمُ - وَخِفَّةَ مَؤُونَتِهِ وَيَسَارَتِهِ يَقُولُ نَصُومُ يَوْمًا مَكَانَهُ .
Yahya related to me from Malik from Zayd ibn Aslam from hisbrother Khalid ibn Aslam that Umar ibn al-Khattab once broke thefaston a cloudy day thinking that evening had come and the sun had set.Then a man came to him and said, "Amir al-muminin, the sun has comeout,'' and Umar said, "That's an easy matter. It was our deduction(ijtihad)." Malik said, "According to what we think, andAllah knows best, what he was referring to when he said, 'That's aneasy matter' was making up the fast, and how slight the effortinvolved was and how easy it was. He was saying (in effect), 'We willfast another day in its place.' " Translation Not Available
Book Ref: Muwatta Imam Malik Book 18 Hadith 677
Web Ref: Muwatta Imam Malik Book 18 Hadith 44