It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: "There is no marriage without a guardian; and if there is no guardian and they dispute, then the ruler (sultan) is the guardian of the one who has no guardian."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13607