It is narrated from Ibn Umar (may Allah be pleased with him) that he said: "When a man makes an oath of abstinence (ila) from his wife, divorce does not take place, even if four months pass, until he is made to stand (before the judge) so that he either divorces her or takes her back."
Hadith Referenceمسند الإمام الشافعي / كتاب عشرة النساء والإيلاء والخلع / 1230
Hadith Takhrijاخرجه البخارى الطلاق، باب قول الله تعالى ﴿لِلَّذِيْنَ يُؤْلُوْنَ مِنْ نِّسَآىٕهِمْ تَرَبُّصُ اَرْبَعَةِ اَشْهُرٍ﴾ (5291)۔