question #2 Sahih al-Bukhari 1911, Book 30, Hadith 21 : How does the Islamic calendar account for months with 29 days?

Allah’s Messenger (ﷺ) vowed to keep aloof from his wives for one month, and he had dislocation of his leg.
So, he stayed in a Mashruba for 29 nights and then came down. Some people said, “O Allah’s Messenger (ﷺ)!
You vowed to stay aloof for one month,” He replied, “The month is of 29 days.”