‘When you see the new crescent, fast, and when you see it, stop fasting. If it is cloudy then calculate it (as thirty days).” Ibn ‘Umar used to fast one day before the new crescent was seen.
Sunan Ibn Majah Book 7, Hadith 17
← Previous Hadith “My paternal uncles among the Ansar who were among the Companions of the Messenger of Allah (ﷺ) told me: ‘The new crescent of Shawwal was covered with clouds, so we fasted the next day. Then some riders came at the end of the day and testified to the Prophet (ﷺ) that they had seen the new crescent the night before. The Messenger of Allah (ﷺ) commanded them to break their fast and to go out to offer the ‘Eid prayer the following morning.’”

Sunan Ibn Majah Book 7, Hadith 16 Next Hadith → “When you see the new crescent then fast, and when you see it then stop fasting. If it is cloudy then fast thirty days.”

Sunan Ibn Majah Book 7, Hadith 18