Sayyidah Aishah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "There is no marriage without a guardian and two upright witnesses. If they dispute, then the ruler is the guardian of the one who has no guardian. If she married (herself), her marriage is void."
(b) Hadrat Umar bin al-Khattab (may Allah be pleased with him) said: Without a guardian and two upright witnesses, marriage is void.
(c) The report that Hadrat Umar bin al-Khattab (may Allah be pleased with him) permitted the testimony of a man together with women in marriage, narrated by Hajjaj bin Artah from Ata, is not sound.
Ata's narration from Umar is munqati' (broken), and Hajjaj bin Artah is not used as proof; the mursal report of Ibn al-Musayyib from Umar (may Allah be pleased with him) is more authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20526