It is narrated from Ali (may Allah be pleased with him) regarding the man who, after divorcing his wife, appointed someone as a witness to his taking her back, while his wife was not aware of it. He said: This woman belongs to the first husband, whether the second has had intercourse with her or not.
Hadith Referenceمسند الإمام الشافعي / كتاب الرجعة / 1285
Hadith Takhrijاسناده صحیح اخرجه البيهقي: 7/373- وفي المعرفة السنن والآثار له (4503) وابن ابي شيبة (18898)۔