See the following reference for more details:
The long and the short of it is that the paper concludes that the Quran does not criticize the Holy Trinity!
Q4:171 and 5:73 instruct the hearer not to say “three,” but according to ibn Hisham (“official” biographer of Muhammad), those verses were spoken at the occasion of a visit to meet with Muhammad in Yathrib/Medinah by the bishop of Najran, Abu Haritha b. Alqama in 631.
In 563, Jacob Baradaeus – head of the Ghassanid church of miaphysite Christians – condemned the doctrine of “tritheism” that was widespread among Arab Christian clergy. This heretical doctrine of tritheism was originated by John Philoponus, who died in 565. It was a monophysitic movement that claimed that the trinity was in fact three gods, not one. Baradaeus had consecrated two monks, Conon of Tarsus and Eugenius of Seleucia. When they left Baradaeus, they went into Arabia, preaching tritheism based on the teachings of John Philoponus.
The Arabic word for Trinity (“al thaluth”) was in widespread use, and would have been known to Muhammad’s learned uncle, Waraqa ibn Nawfal (who stayed Christian and whom Muhammad is said to defend from condemnation). Yet nowhere in the Quran does that term appear.
It would seem that later Muslims got the teachings of the Quran wrong!