Is Islam right about Christians believing in three gods?

Is Islam right about Christians believing in three gods? I don’t mean what people think their religion teaches.  And I’m certainly not talking about what people think, regardless of what their religion teaches.  What I’m looking for is this: what do the scriptures of Islam and Christianity actually say?

Ultimately, this question will decide whether or not the two religions can possibly believe in the same “God”.

Christianity says nothing about Islam at all.  Nothing.  Given that Muhammad wasn’t born until hundreds of years after the last book in the Christian Bible was written, that’s not surprising.

On the other hand, the Qur’an does talk about Christianity.