Someone like him does not fast unless he resolves to fast before dawn.
قال الحارث بن مسكين قراءة عليه وأنا أسمع عن ابن القاسم قال حدثني مالك عن ابن شهاب
مثله لا يصوم إلا من أجمع الصيام قبل الفجر
[Its chain of transmission is daif due to a break in it] It is in Kubra, hadith no. 2650, and its basic version has already appeared, hadith no. 2338.