Sunan an-Nasa'i 2122
سنن النسائي#2122SahihIt was narrated form Ibn 'Umar that the Prophet said:"D not fast until you see it , 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 ZaiIsnaad Sahih
In-book reference: 22:33