On the authority of Ibn Abbas (may Allah be pleased with him), that the Messenger of Allah (Saw) said:
Were people to be given everything that they claimed, men would unjustly claim the wealth and lives of other people. But, the onus of proof is upon the claimant, and the taking of an oath is upon him who denies.
A hasan hadeeth narrated by al-Baihaqee and others in this form, and part of it is in the two Saheehs.
عَنْ ابْنِ عَبَّاسٍ رَضِيَ اللَّهُ عَنْهُمَا أَنَّ رَسُولَ اللَّهِ صلى الله عليه و سلم قَالَ: «لَوْ يُعْطَى النَّاسُ بِدَعْوَاهُمْ لَادَّعَى رِجَالٌ أَمْوَالَ قَوْمٍ وَدِمَاءَهُمْ، لَكِنَّ الْبَيِّنَةَ عَلَى الْمُدَّعِي، وَالْيَمِينَ عَلَى مَنْ أَنْكَرَ» . حَدِيثٌ حَسَنٌ، رَوَاهُ الْبَيْهَقِيّ [في»السنن» 10/252]، وَغَيْرُهُ هَكَذَا، وَبَعْضُهُ فِي «الصَّحِيحَيْنِ».
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