Musannaf Ibn Abi Shayba 13:2925

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: ‘Umar bin Rashid narrated to us, from Yahya bin Abi Kathir, from Abu Salamah bin ‘Abd al-Rahman, he said: "The testimony of one religious community is not permissible against another religious community, except for the Muslims." Waki’ said: Ibn Abi Layla would not permit the testimony of a Jew against a Christian, nor a Christian against a Jew.