Praise be to Allaah.
This insinuating whisper will not have any effect on him. The Prophet (peace and blessings of Allaah be upon him) told us that the Shaytaan comes to a person and says to him “Who created such and such? Who created such and such?” until he says, “Who created Allaah?” The Messenger of Allaah (peace and blessings of Allaah be upon him) has told us of the best medicine for dealing with that, which is to seek refuge with Allaah from the accursed Shaytaan and to put a stop to that.
So if any such thing occurs to you or crosses your mind, say “A’oodhu Billaahi min al-Shaytaan ir-rajeem (I seek refuge with Allaah from the accursed Shaytaan)” and give up this thought and ignore it completely. Then it will go away by Allaah’s Leave.