Muslims hold that the Islamic version of dissimulation is applied only externally with the tongue and not internally (on the heart, spirit, and soul). In other words, a Muslim is allowed to say untruths to a non-Muslim if in their heart they still respect the truths that they externally deny.
Taqiyya, like any other Islamic tenet, has guidelines and limits. However, these guidelines vary from group to group; no single interpretation of this facet of Islamic law is accepted by all groups of Muslims.
According to many Shiite Muslims, dissimulation can only be legally used by Muslims verbally, when a Muslim believes that he or she is being wrongly persecuted. The situation, for example, may be: if no matter whichever course of action an individual chooses, and he has to commit an evil, then reason says that he should select the lesser evil. Islamic scholars claim that there is reason and just leniency for faith to be safeguarded in such situations. The Qur'an states that if one lies, then the lier is guilty of sin and is a transgressor "except he who is compelled while his heart remains steadfast with the faith".
The first use of Taqiyya found historically in Islam was when Muslims were beginning to be tortured by the Quraishites. 'Ammar bin Yasir, a follower of Muhammad, whose friends had been killed for being Muslim by the Quraish, was confronted by a Quraishite. 'Ammar, using Taqiyya, pretended to renounce Islam and thus saved his life when asked if he was a Muslim. Muhammad himself was known to have used Taqiyya when he kept his prophetic mission hidden for three years from the Quraish during their prolonged hostility toward Muslims. As a result, the Islamic religion prospered in Makkah and many lives were spared, making emigration to Medina possible during that time.