Trinity is denied in the Qur’an

People of the Book. Do not go to excess in your religion. Say nothing but the truth about Allah. The Messiah, Jesus son of Maryam, was only the Messenger of Allah and His Word, which He cast into Maryam, and a Spirit from Him. So believe in Allah and His Messengers. Do not say: "Three." It is better that you stop. Allah is only One God. He is too glorious to have a son! Everything in the heavens and in Earth belongs to Him. Allah suffices as a Guardian. The Messiah would never disdain to be a servant to Allah, nor would the angels near to Him. If any disdain to worship Him and grow arrogant, He will, in any case, gather them all to Him. (Surat an-Nisa': 171-72)

Those who say that the Messiah, son of Maryam, is Allah are unbelievers. The Messiah said: "Tribe of Israel. Worship Allah, my Lord and your Lord. If anyone associates anything with Allah, Allah has forbidden him the Garden and his refuge will be the Fire." The wrongdoers will have no helpers. (Surat al-Ma'ida: 72)

Those who say: "Allah is the Messiah, son of Maryam," do not believe. Say: "Who possesses any power at all over Allah if He desires to destroy the Messiah, son of Mary, and his mother, and everyone else on Earth?" The kingdom of the heavens and Earth, and everything between them, belongs to Allah. He creates whatever He wills. Allah has power over all things. (Surat al-Ma'ida: 17)
 

And when Allah asks: "Jesus son of Maryam! Did you say to people: 'Take me and my mother as deities besides Allah?’” He will respond: "Glory be to You! It is not for me to say what I have no right to say! If I had said it, You would have known it. You know what is in my self, but I do not know what is in Your Self. You are the Knower of all unseen things." (Surat al-Ma'ida: 116)

He [Jesus] said: "I am the servant of Allah. He has given me the Book and made me a Prophet. He has made me blessed wherever I am and directed me to perform prayer and give the alms as long as I live…" (Surah Maryam: 30-31)

It is not right for any human being that Allah should give him the Book and Judgment and Prophethood, and then that he should say to people: "Worship me rather than Allah." Rather, he will say: "Be people of the Lord because of your knowledge of the Book, and because you study." (Surah Al 'Imran: 79)

The Messiah, the son of Maryam, was only a Messenger, before whom other Messengers came and went. His mother was a woman of truth. Both of them ate food. See how We make the signs clear to them! Then see how they are perverted! (Surat al-Ma’ida, 75)

We sent no Messenger before you without revealing to him: ‘There is no god but Me, so worship Me.’ They say, ‘The All-Merciful has a son.’ Glory be to Him! No, they are honored servants! They do not precede Him in speech and they act on His command. He knows what is in front of them and what is behind them. They only intercede on behalf of those with whom He is pleased, and even they are apprehensive out of fear of Him. Were any of them to say, ‘I am a god apart from Him,’ We would repay him with Hell. That is how We repay wrongdoers. (Surat al-Anbiya’, 25-29)