In terms of the Shari'ah the two words, Imaan and Islam , are inextricably interwoven. The Shar'i meaning of the one is incomplete without the meaning of the other. The two terms are complementary. The one is a necessary corollary of the other. The existence of the one is dependent on the existence of the other. Negation of the one implies the automatic negation of the other. A proper understanding of Imaan is, therefore, possible only by a study of the Shar'i definition of both words and their interrelationship to one another.
Imaan literally means:
to verify, to accept, to attest with the heart .
Islam literally means:
to submit oneself to another; to make oneself lowly in the presence of another .
In the literal meanings of the two words have their share in the Shar'i definition of Imaan and Islam. Basing the technical (i.e. the Shar'i ) meanings on the literal meanings. Imaam Abu Muhammad Mas'ud Baghawi Rahmatullah Alay says:
Nabi (SAW) defined Islaam as the name for external acts and Imaan as the name of the internal beliefs.
Technical ( Shar'i ) Meaning
For all practical purposes, Imaan and Islaam mean one and the same thing. Allamah Taftaazaani Rahmatullah Alay in sharhul Aqaa-id states:
Imaan and Islaam are on thing.
Imaam Subki Rahmatullah Alay explaining the interrelationship between Imaan and Islaam , says that although Islaam applies to outward submission inward Imaan is a prerequisite or a condition (shart) for its ( Islaam 's) validity. Similarly, although Imaan applies to inward submission (inqiyaad baatin ), outward submission is essential for it.
It will now be clear that Islaam minus Imaan and Imaan without Islaam are of no consideration in the Shari'ah . Allamah Zubaidi rahmatullah Alay states that the Ashaa'irah * and Hanafiyah are unanimous on this view.
The unity of the Shar'i conception of the two words is amply borne out by the following statements which appear in Sharhul Aqaa`id :
In the Shari'ah it is not proper, to proclaim the same person to be a Mu'min but not a Muslim or a Muslim but not a Mu'min.
The one is inseparable from the other because of the unity of conception.
In short Imaan cannot be divorced from Islaam nor Islaam from Imaan .
The accepted and popular definition of Imaan is:
Acceptance with the heart and the declaration with the tongue.
To accept with the heart. To declare with the tongue what has been accepted with the heart. Should anyone of these two fundamentals be lacking, one will not be called a Muslim in the terminology of the Shari'ah .
Difference Between The Two Fundamentals
Of the two fundamentals of Imaan or Islaam , acceptance with the heart ( Tasdeeq bil Qalb ) is the primary one, having greater importance, than declaration with the tongue ( Iqraar bil Lissaan). There is absolutely no possibility of the first fundamental, viz. Tasdeeq bil Qalb , ever being waived whereas the second fundamental, viz. Iqraar bil Lissan , can at times be waived, e.g. the circumstance of torture. Under torture concealing one's Imaan by refraining from declaration with the tongue or by rejecting with the tongue will be permissible on condition that acceptance with the heart remains intact.