It is narrated from Hazrat Umm Hani that once the Prophet (peace be upon him) came to her, asked for water, and drank it. Then he handed the vessel to her, and she also drank its water. Then she remembered and said, "O Messenger of Allah, I was fasting." The Prophet (peace be upon him) said, "If it was a missed fast of Ramadan, then make up for it, and if it was a voluntary fast, then it is up to you—if you wish, make up for it, and if you wish, do not."