Imām Al-Awzā’ī – Allāh have mercy on him – said:
Faith (īmān) is not sound except with [correct] words. Faith and words are not sound except with [good] works. And faith, words and deeds are not sound except with [the correct] intentions in conformance to the Sunnah. Those who went before us of our Salaf did not separate faith from deeds: deeds are a part of faith, and faith is from [ones deeds]. īmān is a word that brings together these aspects of the religions [of Allāh] and is confirmed through [a person’s] works.
So whoever believes in word, knows in his heart and confirms [his belief] through his works, then this is the strongest handhold that will never break. And whoever says [words of faith] but does not know [faith] in his heart nor confirms it with his works, it will never be accepted of him and he will be in the hereafter from those who suffer in loss.
Ibn Ba tt ah, Al-Ibānah Al-Kubrā article 1097.