The Book of Judicial Decisions
حَدَّثَنِي أَبُو الطَّاهِرِ، أَحْمَدُ بْنُ عَمْرِو بْنِ سَرْحٍ أَخْبَرَنَا ابْنُ وَهْبٍ، عَنِ ابْنِ جُرَيْجٍ، عَنِ ابْنِ أَبِي مُلَيْكَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " لَوْ يُعْطَى النَّاسُ بِدَعْوَاهُمْ لاَدَّعَى نَاسٌ دِمَاءَ رِجَالٍ وَأَمْوَالَهُمْ وَلَكِنَّ الْيَمِينَ عَلَى الْمُدَّعَى عَلَيْهِ " .Ibn Abbas reported Allah's Apostle (ﷺ) as saying:If the people were given according to their claims, they would claim the lives of persons and their properties, but the oath must be taken by the defendant
From Sahih Muslim, whose reports the scholars accept as authentic.