Jabir ibn Abdullah reported that Allah's Messenger (peace and blessings of Allah be upon him) visited Umm Sa'ib and said:

“Umm Sa'ib, why is it that you are shivering? She said:" It is fever and may it not be blessed by Allah, whereupon he said: Don't curse fever for it expiates the sin of the children of Adam just as furnace removes the alloy of iron.”

Reported by Muslim.

A believer should not insult the disease.

Here we must pay special attention to the Prophet's behavior (peace and blessings of Allah be upon him). Not only did he say to her, "Do not curse her fever," but he also told her the wisdom of the illness:

“Don't curse fever for it expiates the sin of the children of Adam just as furnace removes the alloy of iron.”

Is it possible for a Muslim to curse what clear his own sins? On the contrary, he should be grateful.