Is the one who insists on sin, and intends in his heart never to abandon it, considered a disbeliever (kafir) with the disbelief of defiance (kufr iba')?

"Kufr al-Iba'" (disdainful disbelief) is the act of defying the Sharia and being arrogant about accepting it, despite acknowledging that it is from Allah. Examples include the disbelief of Iblis, Abu Talib, and the Jews. As for a Muslim who persists in sins, this is not "kufr al-iba'," as there is no necessary correlation between persisting in sin and disbelief, nor does it affect the acceptance of good deeds. Repentance for one sin is valid even while persisting in another. The view that one who persists in sins is not to be declared a disbeliever is the doctrine of Ahl al-Sunnah, and disagreeing with this is a stain from the doctrine of the Khawarij.