Why do signs of a bad end appear on negligent Muslims after death, but not on disbelievers? And does a disbeliever's smile after death indicate anything?

The darkening of the face at death may occur due to illness or other reasons, and this applies equally to the believer and the disbeliever. Therefore, one should not judge a person whose face has darkened as having a bad ending, as a disbeliever may die without their face darkening.

Ibn al-Arabi said: "The face of the deceased is covered only because their face might undergo a frightening change due to illness, leading those who lack knowledge to harbor impermissible ill suspicions about them."

Al-Ghamdi mentioned that the darkening and scowling of the face might be due to the dying person seeing the angels of torment. However, he clarified that this cannot be definitively asserted as a sign of a bad ending due to the absence of evidence, and because it might be due to natural causes such as lack of oxygen.