Sayyidah Umm Hani (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) said: "The one who fasts voluntarily has the choice: if he wishes he may fast, and if he wishes he may break it." The chain of this hadith is sahih (authentic), but the two Shaykhs did not record it, and none of the reports that contradict it is established as sahih (in its chain).