Sunan an-Nasa'i 3456

Muhammad bin al-Muthanna informed us; Khalid narrated to us; Humayd narrated to us, from Anas, who said: The Prophet abstained from his wives for a month in an upper room of his. He stayed there twenty-nine nights, then came down. It was said, ‘Messenger of Allah, did you not vow to stay away for a month?’ He said, ‘The month is twenty-nine days.’