Amr bin Shu'ayb narrates from his father, and he from his grandfather (may Allah be pleased with him), that the Prophet (peace and blessings be upon him) said: "The defendant has more right to the oath, as long as no testimony is established for him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الدعوى والبينات / 21222