Sunan an-Nasa'i 2117

Arabic

أَخْبَرَنَا مُؤَمَّلُ بْنُ هِشَامٍ، عَنْ إِسْمَاعِيلَ، عَنْ شُعْبَةَ، عَنْ مُحَمَّدِ بْنِ زِيَادٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ غُمَّ عَلَيْكُمُ الشَّهْرُ فَعُدُّوا ثَلاَثِينَ ‏"‏ ‏.‏

Translation

It was narrated that Abu Hurairah 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 count it as thirty (days)

Authenticity

Sahih · Abu Ghuddah

Reference