Musnad Ahmad Hadith 4866

It is narrated from Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (ﷺ) said: "A month consists of 29 days." The Noble Prophet (ﷺ) indicated with both his hands by showing ten fingers each time, and on the third time, he folded his thumb. When Sayyidah Aisha (may Allah be pleased with her) learned of this hadith, she said: May Allah forgive Abu Abdur Rahman, he made a mistake. In fact, the Noble Prophet (ﷺ) had separated himself from his noble wives for a month, and after 29 days, the Noble Prophet (ﷺ) came down from his upper room. The people said, "O Messenger of Allah! You have come down on the 29th day." The Noble Prophet (ﷺ) said: "Sometimes a month is also of 29 days."