عَنِ ابْنِ أَبِي مُلَيْكَةَ قَالَ: كَتَبَ إِلَيَّ ابْنُ عَبَّاسٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((لَوْ أَنَّ النَّاسَ أُعْطُوا بِدَعْوَاهُمْ، ادَّعَى نَاسٌ مِنَ النَّاسِ دِمَاءَ نَاسٍ وَأَمْوَالَهُمْ، وَلَكِنَّ الْيَمِينَ عَلَى الْمُدَّعَى عَلَيْهِ))
It is narrated from Ibn Abi Mulaykah, he says: Sayyiduna Ibn Abbas (may Allah be pleased with them both) sent me this writing that the Messenger of Allah (peace and blessings be upon him) said: If people were given according to their claims, they would claim the lives and wealth of others, but the oath will be upon the one against whom the claim is made.