It is narrated from Sayyidah Umm Hani (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) came to her, and a vessel was brought to him (peace and blessings be upon him) and he drank from it. She said: O Messenger of Allah! I was fasting, but I disliked returning what you had left over. The Messenger of Allah (peace and blessings be upon him) said: "If it was a make-up fast for Ramadan, then make it up on another day; and if it was voluntary, then make it up, or if you wish, do not make it up."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21358