It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "There is no marriage without a guardian, and whoever has no guardian, the ruler is her guardian."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2260
Hadith Gradingحکم دارالسلام:حسن لغيره، وهذا إسناد ضعيف، الحجاج بن أرطاة مدلس، وقد عنعن ولم يسمع من عكرمة