Sahih Al Bukhari Hadith Number 1911

Narrated Anas: Allah’s Messenger (peace be upon him) 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 (peace be upon him)! You vowed to stay aloof for one month,” He replied, “The month is of 29 days.”