Praise be to Allah
There is no faith unless it is not accompanied by actions and words, both. Hence faith is not valid unless both are present. This is indicated by Quran and Sunnah and the righteous generations agreed upon this.
Ash-Shaafa‘i (may Allah have mercy on him) said: The consensus of the Sahaabah and Taabi‘een, and those who came after them, and our contemporaries, is that faith consists of words, deeds and intentions, and none of the three is valid except with the others.
End quote from Sharh Usool I‘tiqaad Ahl as-Sunnah by al-Laalkaa’i (5/956); Majmoo‘ al-Fataawa(7/209).
Al-Aajurri (may Allah have mercy on him) said:
You should understand – may Allah have mercy on us and you – that the view of the Muslim scholars is that faith is obligatory for all people, and it consists of belief in the heart, affirmation on the tongue, and physical actions (righteous deeds).
Moreover, you should understand that having knowledge and belief in the heart is not sufficient unless it is accompanied by verbal affirmation of faith, and knowledge in the heart and verbal affirmation are not valid unless they are accompanied by physical action (righteous deeds). Once a person combines these three characteristics, then he is a believer. This is indicated by the Qur’an and Sunnah, and the views of the Muslim scholars.
End quote from ash-Sharee‘ah (2/116).
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: Based on this issue, we may conclude two things, the first of which has to do with visible disbelief and the second has to do with hidden disbelief.
The issue of the hidden disbelief is based on the view that faith consists of both words and deeds as stated above. For the one with the sound belief, he is enjoined to follow the acts of worship. It is not possible for a believer to believe and not prostrate once, never pay any zakaah, never fast or going to holy pilgrimage to Allahs house. These actions are required to be done on the part of faith of a man for the sake of Allah. Leaving all this cannot happen unless the person harbours hypocrisy in his heart. It does not happen when there is sound faith.
Tawheed exists in the heart, which is knowledge and on the tongue, which is in words(verbal affirmation) and in one's actions, which is acting in accordance with what Allah and His Messenger has revealed. If a person does not fulfil one of these three, then he is not a Muslim. He must possess all forms of tawheed in order to be called as a Muslim. A person cannot say He believes but never acts like one. A person cannot keep his faith in is heart and be scared or shy to reveal it. If such is the case then he is not a Muslim. He is a hypocrite.
If he affirms Tawheed but does not act in accordance with it, then he is a stubborn disbeliever, like Pharaoh and Iblees. If he acts outwardly in accordance with Tawheed, but does not believe in it in his heart, then he is a pure hypocrite, worse than a disbeliever. And Allah knows best.
The validity of religious commitment depends on what is in the heart of belief, love and hate, and it depends on a person uttering (the word of Islam, the Shahaadah) and refraining from uttering words of disbelief, and it depends on physical deeds, by putting the pillars of Islam into action, and refraining from deeds that render one a disbeliever. If one of these three is missing, then the person becomes a disbeliever and an apostate.
Physical action is an essential part of faith, without which faith is not valid, and a lack of physical activity is indicative of a lack of faith in the heart, because they are strongly interconnected. Whoever thinks that there could be strong and sound faith without that leading to physical action (righteous deeds), even though he knows about his religious duties and is able to do them, is thinking that something impossible is possible, and is denying the connection between physical activity and what is in the heart.
And Allah knows best.