﴿ وَإِذَا قَرَأْتَ ٱلْقُرْءَانَ جَعَلْنَا بَيْنَكَ وَبَيْنَ ٱلَّذِينَ لَا يُؤْمِنُونَ بِٱلْءَاخِرَةِ حِجَابًۭا مَّسْتُورًۭا ﴾

“But [thus it is:] whenever thou recitest the Qur'an, We place an invisible barrier between thee and those who will not believe in the life to come: -”

And when you recite the Qur’ān We place between you and those who do not believe in the Hereafter a hidden barrier that is one that hides you from them so that they cannot see you — this was revealed regarding those who wanted to assassinate him s the Prophet.