The Messenger of Allah said: "Whichever woman married without the permission of her Wali her marriage is invalid, her marriage is invalid, her marriage is invalid. If he entered into her, then the Mahr is for her in lieu of what he enjoyed from her private part. If they disagree, then the Sultan is the Wali for one who has no Wali."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ أَيُّمَا امْرَأَةٍ نُكِحَتْ بِغَيْرِ إِذْنِ وَلِيِّهَا فَنِكَاحُهَا بَاطِلٌ فَنِكَاحُهَا بَاطِلٌ فَنِكَاحُهَا بَاطِلٌ فَإِنْ دَخَلَ بِهَا فَلَهَا الْمَهْرُ بِمَا اسْتَحَلَّ مِنْ فَرْجِهَا فَإِنِ اشْتَجَرُوا فَالسُّلْطَانُ وَلِيُّ مَنْ لاَ وَلِيَّ لَهُ  

The Messenger of Allah ﷺ said: The marriage of a woman who marries without the consent of her guardians is void. (He said these words) three times. If there is cohabitation, she gets her dower for the intercourse her husband has had. If there is a dispute, the sultan (man in authority) is the guardian of one who has none. (Using translation from Abū Dāʾūd 2083)   

قَالَ رَسُولُ اللهِ ﷺ 10 أَيُّمَا امْرَأَةٍ نَكَحَتْ بِغَيْرِ إِذْنِ وَلِيِّهَا فَنِكَاحُهَا بَاطِلٌ فَإِنْ أَصَابَهَا فَلَهَا مَهْرُهَا بِمَا أَصَابَ مِنْ فَرْجِهَا وَإِنْ اشْتَجَرُوا فَالسُّلْطَانُ وَلِيُّ مَنْ لَا وَلِيَّ لَهُ  

"أيُّمَا امْرَأة نُكِحَتْ بِغَيرٍ إِذن وَليَّهَا فِنَكَاحُهَا بَاطِلٌ، فَنَكَاحُهَا بَاطِلٌ، فَنِكَاحُهَا بَاطِلٌ، فَإِنْ دَخَلَ بِهَا فَلَها المهْرُ بِمَا اسْتَحَلَّ مِنْ فَرْجِهَا، فَإِن اشْتَجَرُوا فالسُّلطَانُ وَلِيُّ مَنْ لا وَلِيَّ له".