5:14
From those, too, who call themselves Christians, We did take a covenant, but they forgot a good part of the message that was sent them: so we estranged them, with enmity and hatred between the one and the other, to the day of judgment. And soon will Allah show them what it is they have done.
Yusuf Ali interprets the concept of the Christian covenant as referring to the charge that Jesus gave to his disciples and that they accepted as part of their mission. In his commentary, he suggests that this covenant included the anticipation of the coming of Ahmad (interpreted in Islamic tradition as a reference to the Prophet Muhammad), an idea which he believes can be found in certain passages of the Gospel of John, such as John 15:26 and John 16:7 (Yusuf Ali, 1934). According to this interpretation, those who identify themselves as Christians but reject this expectation are viewed as departing from what Yusuf Ali considers the original message. In contrast, he suggests that those who acknowledge this prophetic continuity would represent the more authentic followers of that covenant. Yusuf Ali further notes that historical tensions between groups identifying as Christians and Jews are referenced in the commentary as persisting through time.
References:
Yusuf Ali, Abdullah. Translation and Commentary of the Quran.