‘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.