Al-Aswad narrates from Sayyidah Aishah (may Allah be pleased with her) that she intended to buy Sayyidah Barirah (may Allah be pleased with her). He narrated the hadith, and in it is: The Messenger of Allah (peace and blessings be upon him) gave her the choice, and she chose herself (separation). Al-Aswad said: Her husband was free.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14277