The Prophet (peace and blessings be upon him) said: "Any woman who is married without the permission of her guardian and without two upright witnesses, her marriage is void. If he has had intercourse with her, she is entitled to the dower; and if the guardians dispute among themselves, then the ruler is the guardian of the one who has no guardian."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13717