(And it was not (vouchsafed) to any mortal that Allah should speak to him unless (it be) by revelation or from behind a veil...) [42:51].
The Jews said to the Prophet, Allah bless him and give him peace: “Do you not speak [directly] with Allah and look at Him as did Moses? This is if you are really a Prophet. We will never believe in you until you do that”. He said: “Moses did not look at Allah, exalted is He”. Then, Allah, exalted is He, revealed this verse.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou