Surah 5:51
"You who believe! Do not take the Jews and the Christians as allies. They are allies of each other. Whoever of you takes them as allies is already one of them. Surely God does not guide the people who are evildoers."
5.51 – You who believe! Do not take the Jews and the Christians as allies
The seemingly friendly tone in the preceding verses toward the Torah and the Gospel (vv. 43–47) does not carry over to the description of the custodians of those scriptures (see also v. 57; cf. vv. 55–56). Instead, a passage of polemic against the People of the Book seems to develop in verses 48–50 and to continue up to verse 86.
- from The Quran with Christian Commentary: A Guide to Understanding the Scripture of Islam