salams
the hadith is
Narrated Abu Huraira: The people of the Scripture used to read the Torah in Hebrew and explain it to the Muslims in Arabic. Then Allah's Apostle said, "Do not believe the people of the Scripture, and do not disbelieve them, but say, 'We believe in Allah and whatever has been revealed...' (3.84)
Sahih Bukhari
Volume 9, Book 93, Number 632:
tc salam
ps: obviously if Allah told us about something he revealed in the bible (e.g. oneess of Allah) and then a christian comes along tells us about the trinity, there's no reason to remain neutral... because we know for fact the original bible didnt teach the trinity from what the quran said..
salam