Hadith
أَخْبَرَنَا أَبُو دَاوُدَ، قَالَ حَدَّثَنَا يَزِيدُ، أَنْبَأَنَا شَرِيكٌ، عَنْ طَلْحَةَ بْنِ يَحْيَى بْنِ طَلْحَةَ، عَنْ مُجَاهِدٍ، عَنْ عَائِشَةَ، قَالَتْ دَارَ عَلَىَّ رَسُولُ اللَّهِ صلى الله عليه وسلم دَوْرَةً قَالَ " أَعِنْدَكِ شَىْءٌ " . قَالَتْ لَيْسَ عِنْدِي شَىْءٌ . قَالَ " فَأَنَا صَائِمٌ " . قَالَتْ ثُمَّ دَارَ عَلَىَّ الثَّانِيَةَ وَقَدْ أُهْدِيَ لَنَا حَيْسٌ فَجِئْتُ بِهِ فَأَكَلَ فَعَجِبْتُ مِنْهُ فَقُلْتُ يَا رَسُولَ اللَّهِ دَخَلْتَ عَلَىَّ وَأَنْتَ صَائِمٌ ثُمَّ أَكَلْتَ حَيْسًا . قَالَ " نَعَمْ يَا عَائِشَةُ إِنَّمَا مَنْزِلَةُ مَنْ صَامَ فِي غَيْرِ رَمَضَانَ - أَوْ غَيْرِ قَضَاءِ رَمَضَانَ أَوْ فِي التَّطَوُّعِ - بِمَنْزِلَةِ رَجُلٍ أَخْرَجَ صَدَقَةَ مَالِهِ فَجَادَ مِنْهَا بِمَا شَاءَ فَأَمْضَاهُ وَبَخِلَ مِنْهَا بِمَا بَقِيَ فَأَمْسَكَهُ " .
It was narrated that 'Aishah said:"The Messenger of Allah passed by my door. He said: 'Do you have anything (to eat)?' I said 'I do not have anything.' He said 'Then I am fasting.' Then he passed by my door a second time and we had been given some Hais. I brought it to him and he ate, and I was surprised. I said: 'O Messenger of Allah, you were fasting, then you ate Hais.' He said: 'Yes, O 'Aishah. The one who observes a fast other than in Ramadan, or making up a missed Ramadan, fast, is like a man who allocated some of is wealth to give in charity; if he wishes he may go ahead and give it, and if he wishes he may keep it
Hasan · Abu Ghuddah
Sunan an-Nasa'i 2323 ·Book 22, Hadith 234·Also available on sunnah.com·