سُنَنُ النَّسَائِيِّ
Sunan an-Nasa’i 2140
The Book of Fasting
Mentioning The Differences Reported From Yahya Bin Abi Kathir In The Narration Of Abu Salamah about that
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 (ﷺ) 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.
Sunan an-Nasa'i, 2140Sahih (Darussalam)