Sahih Bukhari Volume 003, Book 031, Hadith Number 180.

Narated By Abu Usama from Hisham bin 'Ursa from Fatima : Asma bint Abi Bakr said, "We broke our fast during the lifetime of the Prophet on a cloudy day and then the sun appeared." Hisham was asked, "Were they ordered to fast in lieu of that day?" He replied, "It had to be made up for." Ma'mar said, "I heard Hisham saying, "I don't know whether they fasted in lieu of that day or not."