Muwatta Malik 631
موطأ مالك#631SahihYahya related to me from Malik from Abdullah ibn Dinar from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "A month has twenty-nine days in it. Do not start the fast or break it until you see the new moon. If the new moon is obscured from you, then work out (when it should be)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliSahih
In-book reference: 18:2