Reference: Fataawa Ramadhaan – Volume 1, Page 168, Fatwa No.103
al-Fataawa libni Fowzaan – Kitaab ad-Da’wah, Volume 1, Pages 154-155
Question: On the first night of Ramadhaan [preceding the first day of Ramadhaan], a person went to sleep before knowing that the next day will be the first day of fasting. So, when he woke up [and went] for the Fajr prayer he asked one of the worshipers, who happened to be the last one [left in the masjid] but he did not know. So this man continued as he was and did not eat [or drink] anything. When he reached work he found that the people were fasting and so, only then found out [for definite] about the fasting. So, based on this, he continued in this state and fasted until the evening. Was his fast correct on that day or does he have to make it up?
We request you to give us a fatwa and may Allaah (Subhaanahu wa-Ta’aala) grant you much good.
Response: One who does not know about the arrival of Ramadhaan except during the (first) day, then it is obligatory for him to refrain (from all that breaks the fast, from food and drink etc.) for the rest of the day, then make up that day because he did not make the intention to fast the previous night. And it is mentioned in many ahaadeeth that there is no fast for the one who did not make intention in the night for the obligatory fast. So, with this, some of the day passed whilst he had not made the intention to fast.