However, what is the difference between the profession of the testimony of faith with the tongue and its profession with the heart? Is it obligatory to profess both?
The Answer: The difference between the profession with the tongue and that with the heart is obvious, because some people, like the hypocrites, profess the testimony with their tongues only. As for these hypocrites, Allaah Says concerning them:
Immediately following this, however, Allaah, The Most High, Says:
Those people professed with their tongues but not with their hearts. A person may profess with his heart but does not utter it. This kind of profession does not avail him in as much his profession is not outwardly manifested. As to what is between him and Allaah, then its knowledge is with Allaah, or the ruling on it is with Allaah. However, in as far as the ruling in this life, the profession with his heart alone, does not avail him. It cannot be ruled that he is a Muslim as long as he does not utter the testimony with his tongue, unless he is physically or legally incapable of doing so, then, in this case, he may be dealt with as necessitated by his condition. So, it is inevitable that the testimony be in the heart and on the tongue.