It is narrated from Hazrat Umm Salamah (may Allah be pleased with her) that once the Prophet (peace and blessings be upon him) took an oath that he would not go to his wives for a month. When 29 days had passed, he went to them at some time in the morning or evening. Someone asked, "O Messenger of Allah, you had taken an oath that you would not go to them for a month?" The Prophet (peace and blessings be upon him) replied, "Sometimes a month is also of 29 days."