صحيح مسلم
Sahih Muslim
كتاب الصيام
The Book of Fasting
باب وُجُوبِ صَوْمِ رَمَضَانَ لِرُؤْيَةِ الْهِلاَلِ وَالْفِطْرِ لِرُؤْيَةِ الْهِلاَلِ وَأَنَّهُ إِذَا غُمَّ فِي أَوَّلِهِ أَوْ آخِرِهِ أُكْمِلَتْ عِدَّةُ الشَّهْرِ ثَلاَثِينَ يَوْمًا:
Chapter: The obligation to fast Ramadan when the crescent is sighted, and to break the fast when the crescent is sighted, and that if it is cloudy at the beginning or end of the month, then the month should be completed as thirty days.
Hadith 1080
This hadith is listed as number 2507 in Maktaba Shamila
وحَدَّثَنِي حَجَّاجُ بْنُ الشَّاعِرِ ، حَدَّثَنَا حَسَنٌ الْأَشْيَبُ حَدَّثَنَا شَيْبَانُ ، عَنْ يَحْيَى ، قَالَ : وَأَخْبَرَنِي أَبُو سَلَمَةَ ، أَنَّهُ سَمِعَ ابْنَ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا ، يَقُولُ : سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ : " الشَّهْرُ تِسْعٌ وَعِشْرُونَ " .
Ibn 'Umar (RA) (Allah be pleased with both of them) reported Allah's Messenger (ﷺ) as saying: The month may consist of twenty-nine days.
