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"
Maqtu SahihBook 36 · Hadith 9
موطأ مالك
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"