"Whoever does not have the intention of fasting before dawn, then there is no fast for him."(Daif)
Sunan an-Nasa'i Book 22, Hadith 242
← Previous Hadith "The Messenger of Allah came one day and said: 'Do you have any food?' I said: 'No.' He came in to me on another occasion, and I said: 'O Messenger of Allah, we have been given some Hais.' He said: "Then I will break my fast today, although I had started my day fasting."'

Sunan an-Nasa'i Book 22, Hadith 241 Next Hadith → "Whoever does not have the intention of fasting before dawn, then there is no fast for him." (Daif)

Sunan an-Nasa'i Book 22, Hadith 243