Sunan an-Nasa'i 2121
سنن النسائي#2121SahihIt was narrated from Ibn 'Umar that the Messenger of Allah mentioned Ramadan and said:"Do not fast until you see the crescent, and do not stop fasting until you see it, and if it is obscured from you (too cloudy), then work it out
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 22:32