Nafi' narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both): Any man who takes an oath concerning his wife, when four months pass he is to be made to stand: either he divorces or he takes her back; and divorce does not take effect even after four months have passed, until he is made to stand.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإيلاء / 15218