What is the ruling on acts of worship performed by a person who does not know their rulings and delays learning them due to circumstances or laziness, and is repentance obligatory upon him?

If a person's acts of worship become invalid due to their ignorance of rulings—such as falling into that which invalidates them, or omitting that without which they are not sound—then seeking knowledge of these rulings becomes an individual obligation (fardh 'ayn) upon them, and they incur sin by abandoning it, unless there is an excuse. They must also repent for any negligence. Scholars have differed regarding excusing ignorance in this matter; the majority do not accept it as an excuse, while Shaykh al-Islam was of the view that ignorance is an excuse. As for matters upon which the validity of worship does not depend, these fall under communal obligations (furood al-kifayat). If a sufficient number of people undertake them, then there is no sin in not learning them.