The Prophet (peace and blessings be upon him) said: "There is no marriage without a guardian and two upright witnesses. If a disreputable guardian married her off, then that marriage is void."
Adi bin al-Fadl narrated it thus, and he is da'if (weak); the correct version is mawquf. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13716