ENOfficial
She said that Barira became free when she was with Mughith and God’s Messenger gave her her choice saying, “If he has intercourse with you, you will not be allowed to exercise choice.” Abu Dawud transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْهَا: أَنْ بَرِيرَةَ عَتَقَتْ وَهِيَ عِنْدَ مُغِيثٍ فَخَيَّرَهَا رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَقَالَ لَهَا: «إِنْ قَرِبَكِ فَلَا خِيَارَ لَكِ» . رَوَاهُ أَبُو دَاوُدَ وَهَذَا الْبَابُ خَالٍ عَنِ الْفَصْلِ الثَّالِثِ
sunnah.com