Sayyiduna Umar (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him) said: "The burden of proof is upon the claimant, and the one against whom the claim is made is required only to take an oath."
Hadith Referenceسنن الدارقطني / كتاب فى الأقضية والأحكام وغير ذلك / 4510
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 4510 ، انفرد به المصنف من هذا الطريق»