Musnad Ahmad 1153:2216

Sulayman ibn Hayyan Abu Khalid narrated to us, Hajjaj narrated to us, from al-Zuhri, from Urwah, from Aisha, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "There is no marriage except with a guardian, and the ruler is the guardian of the one who has no guardian."