Were people to be given everything that they claimed, some men would (unjustly) claim the properties and blood of (other) people. However, the onus of proof is on the plaintiff and the oath is upon the one who denies the claim. [Al- Bayhaqi]

«لو يُعْطَى الناسُ بدَعْوَاهُم لادَّعى رجالٌ أموالَ قومٍ ودِمَاءَهُم، لكنَّ البينةَ على المدَّعِي واليَمِينَ على من أَنْكَرَ». [صحيح.] - [أخرجه بهذا اللفظ البيهقي في السنن الكبرى. وأخرج البخاري ومسلم بعضه.]