Sunan an-Nasa'i 3455

Ibn 'Abbas said:"One morning, we saw the wives of the Prophet weeping, and each one of them had her family with her. I entered the Masjid and found it filled with people. Then 'Umar, may Allah be pleased with him, came, and went to the Prophet who was in his room. He greeted him with the Salam but no one answered. He greeted him again but no one answered. He greeted him (a third time) but no one answered. So he went back and called out: 'Bilal!' He came to the Prophet and said: 'Have you divorced your wives?' He said: 'No, but I have sworn an oath of abstention from them for a month.' So he stayed away from them for twenty-nine days, then he came and went into his wives