Talhah bin Abdullah bin Awf (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) sent a caller, who went as far as al-Thaniyyah announcing: "The testimony of a disputant and of one who makes accusations shall not be accepted, and the oath is upon the defendant."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20860