Nafi’ reported: A man came to Ibn Umar, may Allah be pleased with him, and he asked about a man who divorces his wife three times, then he marries her to his brother, without any prior agreement from him, in order to make her lawful to him again. Does she become lawful to the first husband? Ibn Umar said, “No, unless it is a marriage she had desired. We used to consider this illegal fornication in the time of the Messenger of Allah, peace and blessings be upon him.”
Source: al-Sunan al-Kubrá lil-Bayhaqī 14189
Grade: Sahih (authentic) according to Al-Dhahabi
عَنْ نَافِعٍ أَنَّهُ قَالَ جَاءَ رَجُلٌ إِلَى ابْنِ عُمَرَ رَضِيَ اللهُ عَنْهُ فَسَأَلَهُ عَنْ رَجُلٍ طَلَّقَ امْرَأَتَهُ ثَلَاثًا فَتَزَوَّجَهَا أَخٌ لَهُ عَنْ غَيْرِ مُؤَامَرَةٍ مِنْهُ لِيُحِلَّهَا لِأَخِيهِ لَهُ تَحِلُّ لِلْأَوَّلِ قَالَ لَا إِلَّا نِكَاحَ رَغْبَةٍ كُنَّا نَعُدُّ هَذَا سِفَاحًا عَلَى عَهْدِ رَسُولِ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ
14189 السنن الكبرى للبيهقي باب ما جاء في نكاح المحلل
6/2782 المحدث الذهبي خلاصة حكم المحدث إسناده صحيح في المهذب
