Yahya related to me from Malik from Abu'z-Zubayr al-Makki that a
case was brought to Umar about a marriage which had only been
witnessed by one man and one woman . He said, "This is a secret
marriage and I do not permit it. Had I been the first to come upon it,
I would have ordered them to be stoned."
Muwatta Malik Book 28, Hadith 28