Sayyidah Aishah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), narrated that he (peace and blessings be upon him) said: "A woman is not to be married without the command of her guardian. If she marries, that marriage is void" (he repeated these words three times). "If he has intercourse with her, she is entitled to the dowry (mahr) of women like her, because of the intercourse; 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 / 13598