It was narrated from Ibn ‘Umar that the Messenger of Allah (ﷺ) said:‘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
Hadith No. 1654
Sunan Ibn Majah
Gradings:
Al-Albani:
Sahih
Muhammad Fouad Abd al-Baqi:
Sahih
Shuaib Al Arnaut:
Sahih
Zubair Ali Zai:
Sahih - Bukhari And Muslim