Mishkat al-Masabih 2076
‘A'isha said:
The Prophet came to visit me one day and asked if I had anything [to eat]. When I said I had nothing he replied, “Then I shall observe a fast.” When he came to me another day and I told him I had been given a present of some hais * he said, “Show me it, for I began the day fasting.” Then he ate. 
*A mixture of dates and clarified butter.

Muslim transmitted it.
وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: دَخَلَ عَلَيَّ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ذَاتَ يَوْمٍ فَقَالَ: «هَلْ عِنْدَكُمْ شَيْءٌ؟» فَقُلْنَا: لَا قَالَ: «فَإِنِّي إِذًا صَائِمٌ» . ثُمَّ أَتَانَا يَوْمًا آخَرَ فَقُلْنَا: يَا رَسُولَ اللَّهِ أُهْدِيَ لَنَا حَيْسٌ فَقَالَ: «أَرِينِيهِ فَلَقَدْ أَصْبَحْتُ صَائِمًا» فَأَكَلَ. رَوَاهُ مُسلم