Abd al-Aziz bin Abi Salamah (may Allah have mercy on him) said that Ruzayq bin Hakim (may Allah have mercy on him) was the governor of Aylah for Umar bin Abd al-Aziz (may Allah have mercy on him). He wrote (to him) that a witness and an oath are found only in the Hijaz. Umar bin Abd al-Aziz (may Allah have mercy on him) wrote: Judge in this way, for it is the Sunnah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20681