Muslim

Jabir (Allah be pleased with her) narrated that the Holy Prophet (ﷺ) separated himself from his wives for a month. (His wives said:) He came to us on the twenty-ninth day, whereupon we said: It is the twenty-ninth (day) today. Thereupon he said: So far as the month is concerned, (and he, with a view to explaining it) flapped his hands thrice, but held back one finger at the last turn.

Abu Zubair is reported to have heard Jabir bin 'Abdullah (Allah be pleased with both of them) as saying: The Apostle of Allah (ﷺ) separated himself from his wives for a month. (His wives said:) He came to us on the morning of the twenty-ninth. Upon this some, of the people said: It is the morning of twenty- ninth (according to our calculation). Upon this the Apostle of Allah (ﷺ) said: The month may also consist of twenty-nine days. The Apostle of Allah (ﷺ) then flapped his bands thrice, twice with all the fingers of both his hand (to indicate twenty-nine) and by the third time with nine (fingers).