Hadith #2143 (Sunan al-Nasa'i)
Book: The Book of Fasting
Narrator(s): ibn Umar, Muhammad bin al-Muthna - al-Zaman محمد بن المثنى أبو موسى - الزمن, Muhammad bin Ja'far Ghandar محمد بن جعفر غندر صاحب الكرابيس, Shu'bah bin al-Hajjaj شعبة بن الحجاج, Uqba bin Hryth al-Tghlby عقبة بن حريث التغلبي الكوفي

“The Messenger of Allah said: The month may be twenty-nine days or it may be thirty. When you see it, then stop fasting, and it is obscured from you (too cloudy), then complete the count.”‘

Source: https://parallelquran.com/hadith/sunan-al-nasai-2143/