Maliks Muwatta Book 036, Hadith Number 006.

Section : Judgement Based on Oaths with One Witness.

From Malik from Abu'z-Zinad that Umar ibn Abd al-Aziz wrote to Abd al-Hamid ibn Abd ar-Rahman ibn Zayd ibn al-Khattab who was the governor of Kufa, "Pronounce judgement on the basis of an oath with one witness."