Sayyiduna Salamah bin Rabi'ah bin al-Muhabbiq (may Allah be pleased with him) narrates: I heard a woman asking the Messenger of Allah (peace and blessings be upon him) about a slave-girl of hers whom her husband had taken with him on a journey and had intercourse with. The Messenger of Allah (peace and blessings be upon him) said: "If he forced her, she becomes free, and he owes the like of her; and if she yielded to him willingly, she remains his slave-girl, and he owes the like of her."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6309