Surah Al-Ma'idah 5:73

لَّقَدْ كَفَرَ ٱلَّذِينَ قَالُوٓا۟ إِنَّ ٱللَّهَ ثَالِثُ ثَلَـٰثَةٍ ۘ وَمَا مِنْ إِلَـٰهٍ إِلَّآ إِلَـٰهٌ وَٰحِدٌ ۚ وَإِن لَّمْ يَنتَهُوا۟ عَمَّا يَقُولُونَ لَيَمَسَّنَّ ٱلَّذِينَ كَفَرُوا۟ مِنْهُمْ عَذَابٌ أَلِيمٌ

They have certainly disbelieved who say, "Allāh is the third of three." And there is no god except one God. And if they do not desist from what they are saying, there will surely afflict the disbelievers among them a painful punishment.

Translation: Saheeh International

Tafsir

They are indeed disbelievers those who say ‘God is the third of three’ gods that is He is one of them the other two being Jesus and his mother and they who claim this are a Christian sect; when there is no god but the One God. …

Excerpt from Tafsir al-Jalalayn, commentary on 5:73, via Quran.com. The reader has the full commentary and 9 more tafsirs.