Amr bin Dinar (may Allah have mercy on him) says that a woman from Banu Bakr bin Kinanah, who was called Bint Abi Thamamah, married Umar bin Abdullah bin Mudarris. Alqamah bin Alqamah Al-Atwari wrote a letter to Umar bin Abdul Aziz (may Allah have mercy on him) (while he was the governor of Madinah) saying: I am the guardian (wali) of this woman and she married without consulting me. Umar annulled this marriage, even though the man had already consummated the marriage with her. He said: Any woman who marries without the permission of her guardian, her marriage is invalid, because the Prophet ﷺ said: "Her marriage is invalid." And if the man has consummated the marriage with her, then she is entitled to a mahr equal to that of women of her status, in exchange for what he has taken from her, according to the decision of the Prophet ﷺ regarding such a woman.
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1141
Hadith Takhrijاسناده ضعيف لعنعنة ابن جريج والجزء المرفوع مرسل: اخرجه البيهقي في المعرفة السنن والآثار (4079)۔ وعبد الرزاق (10484) وابن ابي شيبة (15941)۔