(6) باب مَا جَاءَ أَنَّ الشَّهْرَ يَكُونُ تِسْعًا وَعِشْرِينَ
Ibn Mas`ud said:
"What I fasted with the Prophet that was twenty-nine (days), was more than what we fasted that was thirty."(He said): There are narrations on this topic from `Umar, Abu Hurairah, `A'isha, Sa`d bin Abi Waqqas, Ibn `Abbas, Ibn `Umar, Anas, Jabir, Umm Salamah, Abu Bakrah, that the Prophet (ﷺ) said: "The month is twenty nine (days)."
Reference: Jami` at-Tirmidhi 689
In-book reference: Book 8, Hadith 8
English translation: Vol. 2, Book 3, Hadith 689