A-4.4: Works

A person is not obliged to learn how to perform ablution, the prayer, and so forth, until the act itself is obligatory for him. As for trade, marriage, and so forth, of things not in themselves obligatory, the Imam of the Two Sanctuaries (A: Juwayni), Ghazali, and others say that learning their means and conditions is personally obligatory for anyone who wants to do them. It has also been said that one should not call this knowledge "personally obligatory," but rather say, "It is unlawful to undertake them until one knows the conditions for their legal validity." And this expression is more accurate.