This Koranic ayah (which, ironically Muslims are trained to use all the time for their position) actually plainly states that the Trinity is not three, but instead, it is one, and then proceeds to list out Father, Son, and Spirit
يأهل الكتب لا تغلوا في دينكم ولا تقولوا على الله
إلا الحق إنما المسيح عيسى ابن مريم رسول الله
وكلمته ألقيها إلى مريم وروح منه فءامنوا بالله
ورسله ولا تقولوا ثلثة انتهوا خيرا لكم إنما الله
إله وحد سبحنه أن يكون له ولد له ما في
السموت وما في الأرض وكفى بالله وكيلا
Ya ahla alkitabi la taghloo fee deenikum wala taqooloo AAala Allahi illa alhaqqa innama almaseehu AAeesa ibnu maryama rasoolu Allahi wakalimatuhu alqaha ila maryama waroohun minhu faaminoo biAllahi warusulihi wala taqooloo thalathatun intahoo khayran lakum innama Allahu ilahun wahidun subhanahu an yakoona lahu waladunlahu ma fee alssamawati wama fee al-ardi wakafa biAllahi wakeelan
4.171 You The Book's family, certainly do not go beyond the limits in your faith, and they do not say on allah except The Truth (is) only the Messiah Jesus, Mary's son, allahs messenger, and his Word, cast forth to her, Mary, and Spirit from him; so believe on account of allah, and His messengers, and they do not say: "Three." Refrain (it is) agreeable certainly your only allah one godglory be to him, that He has certainly been his Son,truly His what is in the heavens and what is in the earth and He sufficed on account of allah, a witness.
Observe that this ayah is directed at The Books family (ahla alkitabi) which refers to the followers of the Holy Bible; i.e. Christians.
For the Muslim, it then gives instruction as to what the correct interpretation of the Holy Bible needs to be regarding (among numerous things), the concept of the Trinity.
In this classic Islamic one-hit-wonder we are told not to refer to the one allah as Three, as even his messengers do not say Three - because he is not the result of counted things (thalathatun)
.and yet, in the very ayah itself it lists-out directly, Father, Son, & Spirit.
This is a classic Koranic example in which the authors display their understanding of the Biblical concept of the Holy Trinity, and give the example of what it is not by the usage of the word Three
and what it is, by the example of one.