Translation
(7) Fasting
كتاب الصيام
(8) Chapter: What was narrated concerning: “The month is twenty-nine (days)”
(8) باب مَا جَاءَ فِي الشَّهْرُ تِسْعٌ وَعِشْرُونَ
Sunan Ibn Majah 1657 
It was narrated from Muhammad bin Sa’d bin Abu Waqqas that his father said:
“The Messenger of Allah (ﷺ) said: ‘The month is like that and like that and like that,’ and he showed nine fingers on the third time to indicate twenty-nine.”
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ، حَدَّثَنَا مُحَمَّدُ بْنُ بِشْرٍ، عَنْ إِسْمَاعِيلَ بْنِ أَبِي خَالِدٍ، عَنْ مُحَمَّدِ بْنِ سَعْدِ بْنِ أَبِي وَقَّاصٍ، عَنْ أَبِيهِ، قَالَ: قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ الشَّهْرُ هَكَذَا وَهَكَذَا وَهَكَذَا ‏"‏ ‏.‏ وَعَقَدَ تِسْعًا وَعِشْرِينَ فِي الثَّالِثَةِ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan Ibn Majah 1657
In-book reference : Book 7, Hadith 20
English translation : Vol. 1, Book 7, Hadith 1657