Why did Abraham (peace be upon him) attribute sickness to himself and healing to God, by saying: "And when I am ill, it is He who cures me," even though all قدر (divine decree), both good and bad, is from God? And do prophets fall ill due to their sins? And can it be said that prophets are absolutely infallible from sins?

Allah Almighty is the Creator of all things. No movement or stillness occurs except by His permission and will. He is the Creator of evil for profound reasons, but evil is not from His actions (af'al), rather it is from His creations (maf'ulat). Therefore, evil is not attributed to Allah Almighty in isolation, but rather it falls under generalities, or it is attributed to its cause, or its doer is omitted; this is out of reverence in addressing Allah. The prophets are infallible from condoning sins, and the afflictions that befall them are not due to sin, but for great wisdoms such as elevating their ranks and making them examples for their nations.