Abdullah bin `Umar (May Allah be pleased with them) reported: Messenger of Allah (Sallallahu Alyhi Wa Sallam) said, "I have been commanded (by Allah) to fight people until they testify that there is no true god except Allah, and that Muhammad is the Messenger of Allah, and perform Salat and pay Zakat. If they do so, they will have protection of their blood and property from me except when justified by Islam, and then account is left to Allah". [Al-Bukhari and Muslim]

Commentary: When a person embraces Islam, the laws of Shari`ah apply to him according to his apparent condition only. His heart will not be probed for this purpose. In case, he is not sincere or he has some design in joining the fold of Islam, no action will be taken against him until guilt is fully proved. What he has in his heart will be left to Allah Who will pass judgement on his intention on the Day of Resurrection. In their debate on this point, some `Ulama' have contended that such people who believe in Tauhid and obey the injunctions of Shari`ah are not to be declared as infidels.