The Messenger of Allah ﷺ said, "Any woman who marries without the permission of her guardian, her marriage is invalid, her marriage is invalid, her marriage is invalid. If he has consummated the marriage with her, she is entitled to the dowry in return for what he has made lawful of her private parts. If they dispute, then the ruler is the guardian of one who has no guardian."
حدثنا ابن أبي عمر حدثنا سفيان بن عيينة عن ابن جريج عن سليمان بن موسى عن الزهري عن عروة
أن رسول الله ﷺ قال أيما امرأة نكحت بغير إذن وليها فنكاحها باطل فنكاحها باطل فنكاحها باطل فإن دخل بها فلها المهر بما استحل من فرجها فإن اشتجروا فالسلطان ولي من لا ولي له
[Its chain of transmission is hasan]. Abu Dawud narrated it in Nikah, chapter on the guardian, hadith 2083, from Sufyan bin Uyayna with this wording. Ibn Hibban graded it sahih, hadith 1248, as did Hakim, 2/168, saying it meets the criteria of the two Shaykhs (Bukhari and Muslim). Ibn Adi strengthened it in al-Kamil, 3/1115. Ibn Jurayj heard it from Sulayman, and Sulayman heard it from Zuhri, from Urwa. I have elaborated on its chains of transmission at length in my edition of Musnad Humaydi, hadith 230. The hadith has many corroborating narrations.