Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "No woman should keep even a single (voluntary) fast while her husband is present, except with his permission; Ramadan is a different matter." (Allamah Haythami says:) I say:
This is in the Sahih, but without the words: "Ramadan is a different matter."
Ahmad recorded it, and its chain is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 5219