What is the ruling on one who abandons sins out of fear of a specific worldly punishment, such as the illness of a parent, and is this considered a negative assumption about Allah?

A Muslim's abandonment of sin out of fear that Allah might afflict him with a worldly punishment is prescribed and rewarded. The Quran is full of verses that warn of immediate punishments. Sincerity of intention is not a condition for abandoning sin to escape its punishment; rather, it is a condition for receiving reward. There is no legitimate textual evidence that the disobedient person is punished by his father falling ill. And whoever thinks of Allah that He punishes someone without a crime, then he has thought ill of Him.