(4) باب الشَّهْرُ يَكُونُ تِسْعًا وَعِشْرِينَ
Sa'd b. Abi Waqqas (Allah be pleased with him) said that the Messenger of Allah (ﷺ) struck his hand against the other and (then with the gesture of his two hands) said:
The month is thus, thus (two times). He then withdrew (one of) his fingers at the third turn.
Reference: Sahih Muslim 1086 a
In-book reference: Book 13, Hadith 31
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2389