Jamil bin Abd al-Rahman al-Mu'adhdhin used to attend Umar bin Abd al-Aziz (may Allah have mercy on him) when he was the governor of Madinah and judged between people. When a man made a claim against another, he would look: if he saw that there were dealings and mixing between the two, he would require the defendant to take an oath; and if there were no such dealings between them, he would not require the oath.
Imam al-Shafi'i (may Allah have mercy on him) said in the Book of Claims: The oath is upon the defendant, whether there were dealings between the claimant and the defendant or not.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21209