Allaah (The Most High) said:
أَفَمَن زُيِّنَ لَهُ سُوءُ عَمَلِهِ فَرَآهُ حَسَنًا
Is he, then, to whom the evil of his deeds made fair-seeming, so that he considers it as good (equal to one who is rightly guided)? [Surah Faatir; Ayah 8]
Ibn Abbaas (radiyallaahu-anhumaa) said: This ayah was revealed concerning Abu Jahl and the idolaters of Makkah.
Sa’eed Bin Jubair (rahimahullaah) said: This was revealed concerning the people of bidah and desires.
Qataadah (rahimahullaah) said: And from them (i.e. the people of desires and bidah) are the khawaarij, who make lawful the spilling of the blood of the Muslims and confiscating their wealth. As for the people of the Kabaa’ir (i.e. those sinful Muslims who commit major sins) they are not from them (i.e. not from those whom the evil of their deeds are made fair-seeming, so that they consider it as good) because they do not declare the major sins to be lawful.
The one to whom doubts are made fair-seeming and is submerged in it, and his deeds are made fair-seeming to him, so that he considers it as good, shaytaan makes it fair-seeming to him through waswaas.
[Source: Tafseer Al-Baghawi 3/689]