Does what a person does in terms of wrong decisions that they later regret fall under the saying of the Messenger of Allah, peace and blessings be upon him: "It is the decree of Allah, and what He wills, He does," or under the saying of Allah the Almighty: "Whatever good befalls you is from Allah, and whatever evil befalls you is from yourself"?

All occurrences, good and bad, are by the decree and creation of Allah. This is the belief of Ahlus-Sunnah (definition) wal-Jama'ah (the People of the Sunnah and the Community), and it is supported by His (SWT) saying: "Indeed, We created all things in due measure" and "Allah is the Creator of all things." It is also supported by the saying of the Prophet (peace be upon him): "Everything is by measure, even incapacity and intelligence."

And His (SWT) saying: "Whatever good befalls you is from Allah, and whatever evil befalls you is from yourself," means that blessings are a favor from Allah, and that calamities and adversities are caused by the servant through his disobedience and the evils of his own self. It does not mean that evils are not by Allah's decree.

There is no contradiction between all decrees being by Allah's ordination and what befalls the servant of evils being due to himself. A Muslim must believe in Allah's decree, praise Him for blessings, and repent and seek forgiveness when afflicted by calamity.