Is discontent with the divine decree considered disbelief (kufr)? And what is its expiation?

Patience with Allah's decree and destiny is obligatory, and there is no disagreement regarding that. As for contentment of the heart, there are two opinions among scholars: one makes it obligatory, and the other considers it recommended. Ibn al-Qayyim explained that a sick person who drinks a repulsive medicine, a fasting person in intense heat, and a miser who pays his zakat (definition) are all examples of the co-occurrence of pain with contentment. As for contentment with Allah as a Lord, Islam as a religion, and Muhammad as a messenger, its obligatoriness is agreed upon, and a servant's Islam is not valid without it.