Is testimony regarding the character of an opponent accepted?

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The testimony of an opponent against whom a legal claim has been made regarding their character is not accepted. There is no difference of opinion among the scholars on this matter. If the defendant states that the witnesses against him are wicked (fasiqan), enemies to him, or fathers of the claimant, his statement is not accepted because he is suspect in his declaration, as he seeks to gain a benefit from his statement, resembling self-testimony. If his statement were accepted, anyone against whom a witness testified could invalidate that testimony merely by impugning the witness's character, which would cause rights to be lost and negate the wisdom behind legislating the use of evidence (bayyinah).