The Messenger of Allah ﷺ permitted the testimony of the People of the Book against one another.
حدثنا محمد بن طريف حدثنا أبو خالد الأحمر عن مجالد عن عامر
أن رسول الله ﷺ أجاز شهادة أهل الكتاب بعضهم على بعض
No references are available.
[Its chain is daif] Bayhaqi narrated it, 10/165, from the hadith of Abu Khalid through this chain, and he said, this is among what he erred in. Busiri said, this is a daif chain because of Mujalid bin Saeed. See also hadith 11, which contains another flaw mentioned by Bayhaqi, as noted above in his remarks.