Sunan an-Nasa'i 2124
سنن النسائي#2124SahihIt was narrated that Ibn Abbas said:"The Messenger of Allah said; 'Fast when you see it and stop fasting when you see it, and if it is obscured from you (too cloudy), then complete thirty (days)
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 ZaiIsnaad Sahih
In-book reference: 22:35