An-Nahl 16:106

Man kafara billahi minbaAAdi eemanihi illa man okriha waqalbuhu mutma-innunbil-eemani walakin man sharaha bilkufrisadran faAAalayhim ghadabun mina Allahiwalahum AAathabun AAatheem

Whoever disbelieves in [i.e., denies] Allāh after his belief... except for one who is forced [to renounce his religion] while his heart is secure in faith. But those who [willingly] open their breasts to disbelief, upon them is wrath from Allāh, and for them is a great punishment;

Whoever rejects his faith in Allah after having believed in Him - not the one who is compelled (to utter a word of disbelief) under duress while his heart is at peace with Faith, but the one who has laid his breast wide open for disbelief - upon such people is the wrath of Allah, and for them there is a heavy punishment.