It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (the Prophet) (peace and blessings be upon him) said: "A marriage takes place in the presence of four: 1. the guardian, 2. the one marrying, 3. two upright witnesses."
This has also been narrated through another, weak route from Abu Salamah from Abu Hurayrah as marfu', and through another, weak route from Hisham bin Urwah, from his father, from Aishah (may Allah be pleased with her) as marfu'.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13816