The Prophet ﷺ said, "A woman must not fast on any day outside the month of Ramadan while her husband is present, except with his permission."
حدثنا هشام بن عمار حدثنا سفيان بن عيينة عن أبي الزناد عن الأعرج
عن النبي ﷺ قال لا تصوم المرأة وزوجها شاهد يوما من غير شهر رمضان إلا بإذنه
Sourcing, [sahih] Tirmidhi narrated it in the Book of Fasting, chapter on the dislike of a woman fasting without her husband's permission, no. 782, from the hadith of Sufyan through this chain, and he said, hasan sahih. Bukhari narrated it, no. 5195, from the hadith of Abu Zinad through this chain, with a similar meaning but different wording, with a slight variation.