Ibrahim (may Allah have mercy on him) narrates from Qadi Shurayh (may Allah have mercy on him) that the testimony of a Jew or a Christian against a Muslim is valid only in a bequest, not otherwise, and this too is restricted to travel.
(b) Yahya bin Wathhab (may Allah have mercy on him) says that Qadi Shurayh (may Allah have mercy on him) considered the testimony of the People of the Book against one another permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20630