If a prohibited act is done due to forgetfulness or lack of knowledge, there is no sin, and the Hajj or ‘Umrah is not invalidated. However, in some cases, once the person remembers or becomes aware, they must immediately stop the act, and a kaffarah (expiation) may still be required depending on the specific prohibition. This is the well-known opinion of Shi‘a jurists such as Imam Khomeini and Ayatollah Khamenei.