The Book of Fasting
22/9. Chapter:
Completing thirty days Of Sha'ban if it is obscured (cloudy) and mentioning the differences reported by the narrators from Abu Hurairah
Sunan an-Nasai
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 " .
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). "'
Reference : Sunan an-Nasa'i 2117In-book reference : Book 22, Hadith 28English translation : Vol. 3, Book 22, Hadith 2119