Al-Máida 5:107 فان عثر على انهما استحقا اثما فاخران يقومان مقامهما من الذين استحق عليهم الاوليان فيقسمان بالله لشهادتنا احق من شهادتهما وما اعتدينا انا اذا لمن الظالمين ١٠٧

Then, if it is discovered that the two had rendered themselves liable to a sin, then, in their place shall stand two others, closest of those whose right has been taken away, and they shall swear by Allah, “Our evidence is more truthful than their evidence, and we have not transgressed; otherwise we should be among the unjust.”