(4) باب الشَّهْرِ يَكُونُ تِسْعًا وَعِشْرِينَ
Narrated Abdullah ibn Mas'ud:
We kept fast for twenty-nine days along with the Prophet (ﷺ) more often than we kept fast for thirty days.
Reference: Sunan Abi Dawud 2322
In-book reference: Book 14, Hadith 10
English translation: Book 13, Hadith 2315