Sahih Muslim Book 6, Hadith Number 2552.

Chapter : Permissibility of completing the fasts of Ramadhan before the commencement of the coming Ramadhan.

‘Aisha reported: If one amongst us had to break fasts (of Ramadan due to natural reasons, i.e. menses) during the life of the Messenger of Allah (may peace be upon him) she could not find it possible to complete them so long she had been in the presence of Allah’s Messenger (may peace be upon him) till Sha’ban commenced.