It is narrated from Ibn Abbas (may Allah be pleased with them) that he said: A marriage does not take place without a guardian, a wali, and two trustworthy witnesses.
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1133
Hadith Takhrijصحيح بطرقه اخرجه البيهقي: 7 / 112، 124، 126 - وعبد الرزاق (10483) وابن ابي شيبة (15917)۔