Hadith 2140
Chapter 17: Mentioning The Differences Reported From Yahya Bin Abi Kathir In The Narration Of Abu Salamah about that - كتاب الصيام
أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، عَنْ سُفْيَانَ، عَنِ الأَسْوَدِ بْنِ قَيْسٍ، عَنْ سَعِيدِ بْنِ عَمْرٍو، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " إِنَّا أُمَّةٌ أُمِّيَّةٌ لاَ نَكْتُبُ وَلاَ نَحْسِبُ الشَّهْرُ هَكَذَا وَهَكَذَا وَهَكَذَا " . ثَلاَثًا حَتَّى ذَكَرَ تِسْعًا وَعِشْرِينَ .
It was narrated from Ibn 'Umar that the Prophet said:
"We are an unlettered Ummah, we do not use astronomical counting or computation. The month is like this, and this, and this," he did three times, showing it as twenty-nine.
Reference : Sunan an-Nasa'i 2140
In-book reference : Book 22, Hadith 51