Allah is trying to convince us, that the teaching of trinity is false. When doing so, he happens to teach… the trinity. Oops!
O People of the Book, do not exaggerate in your religion and do not speak against Allah, except the truth. Surely the Christ ‘Isā, son of Mary, is only a messenger of Allah and his word, which he cast to Mary, and a spirit from him. So believe in Allah and his messengers, and do not say, “Three.” Sura 4:171
Ok, let’s break this down.
Surely the Christ ‘Isā, son of Mary, is only a messenger of Allah
Jesus Christ, is a messenger of allah.
and his word
Jesus Christ is the not only a messenger, but the word of allah. “His word”, means allah’s word. Allah’s word is eternal, so therefore Jesus being the eternal word of allah, must be eternal.
which he cast to Mary, and a spirit from him
Conclusion: Jesus Christ is the messenger of allah, the word of allah, and the spirit of allah. Sounds like classic trinity to me.
Islam is false. Allah is a fabricated god made up by a false prophet.