Sunan an-Nasa'i 2120
سنن النسائي#2120SahihAbdullah bin 'Umar said:" I heard the messenger of Allah say: 'When you see the crescent then fast, and when you see it, then stop fasting, and if it is obscured from you (too cloudy), then work it out (fro the beginning of the month, to complete thirty days)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu Ghuddah-
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 22:31