Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "People of different religions cannot inherit from one another, nor can they be witnesses (against one another). But Muslims can testify regarding the followers of every other religion; their testimony is valid against the people of all religions."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20617