(2) بَاب وُجُوبِ صَوْمِ رَمَضَانَ لِرُؤْيَةِ الْهِلَالِ وَالْفِطْرِ لِرُؤْيَةِ الْهِلَالِ وَأَنَّهُ إِذَا غُمَّ فِي أَوَّلِهِ أَوْ آخِرِهِ أُكْمِلَتْ عِدَّةُ الشَّهْرِ ثَلَاثِينَ يَوْمًا
Ibn 'Umar (may Allah be pleased with both of them) reported Allah's Apostle as saying:
We are an unlettered people who can neither write nor count. The month is thus, and thus. folding his thumb when he said it the third time. (ES)
Reference (ES): Sahih Muslim 1080 n (ES)
In-book reference (ES): Book 13, Hadith 17 (ES)
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2376 (ES)