Sahih Muslim Book - 30, Hadith - 4470

حَدَّثَنِى أَبُو الطَّاهِرِ أَحْمَدُ بْنُ عَمْرِو بْنِ سَرْحٍ أَخْبَرَنَا ابْنُ وَهْبٍ عَنِ ابْنِ جُرَيْجٍ عَنِ ابْنِ أَبِى مُلَيْكَةَ عَنِ ابْنِ عَبَّاسٍ أَنَّ النَّبِىَّ -صلى الله عليه وسلم- قَالَ « لَوْ يُعْطَى النَّاسُ بِدَعْوَاهُمْ لاَدَّعَى نَاسٌ دِمَاءَ رِجَالٍ وَأَمْوَالَهُمْ وَلَكِنَّ الْيَمِينَ عَلَى الْمُدَّعَى عَلَيْهِ ».

It was narrated from Ibn 'Abbas that the Prophet (s.a.w) said: "If people were given on the basis of their claims, people would claim the lives and property of men. Rather the oath should be sworn by the defendant."