Ibn Abbas wrote to me that the Messenger of Allah ﷺ ruled that the oath is upon the defendant.
حدثنا عبد الله بن مسلمة القعنبي حدثنا نافع بن عمر
كتب إلي ابن عباس أن رسول الله ﷺ قضى باليمين على المدعى عليه
Bukhari transmitted it, Rahn, chapter "If the pledger and the pledgee disagree, and similar cases..." etc., no. 2514, and Muslim, Aqdiyah, chapter "The oath is upon the defendant," no. 1711, from the hadith of Nafi bin Umar, through this same chain.