لَقَدْ كَفَرَ الَّذِيْنَ قَالُوْٓا اِنَّ اللّٰهَ ثَالِثُ ثَلٰثَةٍ ۘ وَمَا مِنْ اِلٰهٍ اِلَّآ اِلٰهٌ وَّاحِدٌ ۗوَاِنْ لَّمْ يَنْتَهُوْا عَمَّا يَقُوْلُوْنَ لَيَمَسَّنَّ الَّذِيْنَ كَفَرُوْا مِنْهُمْ عَذَابٌ اَلِيْمٌ ( المائدة: ٧٣ )
laqad kafaral lazeena qaalooo innal laaha saalisu salaasah; wa maa min ilaahin illaaa Ilaahunw Waahid; wa illam yantahoo 'ammaa yaqooloona layamas sannal lazeena kafaroo minhum 'azaabun aleem (al-Māʾidah 5:73)
They have certainly disbelieved who say, "Allah 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. (Al-Ma'idah  : 73)
1 Mufti Taqi Usmani
Surely, disbelievers are those who say, “Allah is the third of the three” while there is no god but One God. If they do not desist from what they say, a painful punishment shall certainly befall such disbelievers.