Sayyiduna Miswar bin Makhramah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) set out at the time of the Treaty of al-Hudaybiyyah. In it these words are additional: When believing women came as emigrants, Allah forbade returning them and commanded only that the dowry (mahr) be returned.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18834