What should one do if Satan whispers to him that he has broken his fast while he is fasting during the daytime in Ramadan, after he had intended to fast from the night?

It is advised not to succumb to obsessive whispers (waswas), and their cure lies in ignoring them, holding fast to the remembrance of Allah, fortifying oneself with the Two Protectors (Mu'awwidhatayn), Ayatul-Kursi, and other remembrances (adhkar), utilizing lawful ruqyah (definition), and trusting in Allah and relying on Him. It should be known that the fast is valid as long as one has abstained from things that break the fast with the intention from before dawn, and that the occurrence of obsessive whispers with the intention to break the fast does not affect the validity of the fast. It is also advised not to isolate oneself excessively, but rather to participate with others in iftar (definition) and suhoor (definition).