Sahih Bukhari, Chapter: Oppressions (Al-Mazalim)

Allah's Apostle (SAW) took an oath that he would not go to his wives for one month as his foot had been sprained. He stayed in an upper room when 'Umar went to him and said, "Have you divorced your wives?" He said, "No, but I have taken an oath that I would not go to them for one month." The Prophet (SAW) stayed there for twenty-nine days, and then came down and went to his wives.