Shu'bi narrates that Qadi Shurayh used to accept the testimony of a person belonging to a certain religion against another person of the same religion; he would not accept the testimony of a Jew against a Christian, nor a Christian against a Jew. However, the matter was different regarding Muslims, for he would accept the testimony of any Muslim against all other religions.
Hadith Referenceسنن الدارقطني / كتاب فى الأقضية والأحكام وغير ذلك / 4605