What is the ruling on someone who drank, thinking that the first call to prayer for Fajr had begun, but then it became clear to him that it was the second call to prayer? Should he complete his fast or break it and make it up?

If someone ate or drank, thinking night had fallen, but then realized their mistake, their fast is broken, and they must make up that day. This is the view of the majority of scholars. According to some scholars, they are not required to abstain for the rest of the day if it was a make-up fast.