It was narrated that ‘Aishah said:
“The Messenger of Allah (ﷺ) would enter upon me and say: ‘Do you have anything (any food)?’ If we said: ‘No,’ he would say: ‘Then I am fasting.’ So he would continue fasting, then if we were given some food, he would break his fast.” She said: “Sometimes he would fast and (then) break fast (in one day).” I said: “How is that?” She said: “Like the one who goes out with charity (something to give in charity), and he gives some away and keeps some.”
حَدَّثَنَا إِسْمَاعِيلُ بْنُ مُوسَى، حَدَّثَنَا شَرِيكٌ، عَنْ طَلْحَةَ بْنِ يَحْيَى، عَنْ مُجَاهِدٍ، عَنْ عَائِشَةَ، قَالَتْ دَخَلَ عَلَىَّ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ فَقَالَ: ” هَلْ عِنْدَكُمْ شَىْءٌ؟ ” . فَنَقُولُ: لاَ . فَيَقُولُ: ” إِنِّي صَائِمٌ ” . فَيُقِيمُ عَلَى صَوْمِهِ ثُمَّ يُهْدَى لَنَا شَىْءٌ فَيُفْطِرُ . قَالَتْ: وَرُبَّمَا صَامَ وَأَفْطَرَ . قُلْتُ: كَيْفَ ذَا؟ قَالَتْ: إِنَّمَا مَثَلُ هَذَا مَثَلُ الَّذِي يَخْرُجُ بِصَدَقَةٍ فَيُعْطِي بَعْضَهَا وَيُمْسِكُ بَعْضًا .
Reference : Sunan Ibn Majah 1701
In-book reference : Book 7, Hadith 64
English translation : Vol. 1, Book 7, Hadith 1701