Authentic
graded by Salim al-Hilali
Muwatta Malik 1410
وَعَنْ مَالِكٍ، عَنْ أَبِي الزِّنَادِ، أَنَّ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ، كَتَبَ إِلَى عَبْدِ الْحَمِيدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ زَيْدِ بْنِ الْخَطَّابِ وَهُوَ عَامِلٌ عَلَى الْكُوفَةِ أَنِ اقْضِ بِالْيَمِينِ مَعَ الشَّاهِدِ .
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."
Reported by Malik (No. 1410).