It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) issued the judgement that "when the claimant has no proof (evidence or witness), the defendant (the one against whom the claim is made) is bound to take an oath." These are the words narrated by Imam Ishaq.
The wording of the other narrator (Muhammad bin Bishr) is: "Whoever makes a demand without witnesses, the one from whom it is demanded has the greater right to take the oath."
Imam Ishaq also stated that Abu Mu'awiyah narrated to us from Hajjaj with this same chain a hadith like it.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب القضاء والشهادات / 2189
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :إسناده صحيح. » «انفرد به المصنف من هذا الطريق»