Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates: One day we woke in the morning and the wives of the Prophet (peace and blessings be upon him) were weeping, and with each one of them were members of her family. I went out to the mosque and saw that it was full of people. Sayyiduna Umar (may Allah be pleased with him) came and went up to the Prophet (peace and blessings be upon him), who was in an upper room, and greeted him with salam, but he (peace and blessings be upon him) did not answer. He asked: Have you divorced your wives? He (peace and blessings be upon him) said: "No, but I have taken an oath of ila' (to stay away from them)." He (peace and blessings be upon him) stayed (away) for twenty-nine days, then came down to his family.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12177