What is the legal basis for rejecting conflicting narrations regarding shared paternity?

Primary text

The position that accepts shared paternity is maintained despite a reported narration from Umar where he apparently rejected the ascertainers' finding of shared paternity and told the claimant to choose one father. The scholars upholding the shared paternity ruling assert that the authenticity of this specific narration from Umar is unknown. If it were authentic, it must be interpreted that Umar rejected the ascertainers' testimony due to an overriding factor, such as lacking trust in them, or discovering contradiction or inconsistency in their statements that necessitated dismissing their finding. Therefore, the basis for rejection is not exclusively the impossibility of shared paternity.