All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
This act by itself is not considered Kufr (disbelief). But it is a sin that requires repentance to Allah like other sins.
You have to strive against whispers if you are afflicted with them and do not pay any attention to them.
Allah knows best.