Mufti Zahid Sahib's response: 1. If the matter reaches the clarity of kufr sareeh muta'ayyan to any Muslim, he must do takfeer otherwise doubt will make him a kaafir. 2. If it has not become clear to a person then he may remain quiet. 3. Once something is determined as kufr, it is part of Iman to immediately believe it to be kufr.