Praise be to Allah.
The ruling on placing the Mus-haf (copy of the Quran) in cars to ward off the evil eye and for protection from danger is a bidah. The Sahaabah (may Allah be pleased with them) never carried the Mus-haf to ward off danger or the evil eye. If it is bidah, then we should remember that the Prophet (peace and blessings of Allah be upon him) said: Every bidah is a going-astray and every going-astray will lead to Hell.
(Telephone conversation with Shaykh Muhammad ibn Saalih al-Uthaymeen) (al-Bida wal-Muhdathaat wa maa laa aslun lahu, p. 259).
Shaykh Abd al-Azeez ibn Baaz (may Allah have mercy on him) was also asked the following question: Some people hang up aayaat of the Quran and ahaadeeth of the Prophet (peace and blessings of Allah be upon him) in the rooms of their homes or in restaurants or offices. In some hospitals and doctors offices they hang the aayah (interpretation of the meaning): And when I am ill, it is He Who cures me [al-Shuara 26:80], and so on. Is this considered to be the use of amulets which is forbidden in shareeah, knowing that the intention behind it is to seek blessings and ward off the shayaateen, or to remind the forgetful and warn the negligent? Is it like using amulets to put the Mus-haf in one's car in order to seek blessings?
His Eminence replied as follows:
If the intention is as described, to remind people and teach them something beneficial, then there is no harm in that. But if they believe that it is a protection against the shayaateen or jinn, then I know of no basis for this. By the same token, there is no basis for putting the Mus-haf in one's car to protect it, and doing so is not allowed, but if a person puts it in his car so that he can read it sometimes or so that some of his passengers can read it, then this is good and there is nothing wrong with it. And Allah is the Source of strength.