When Taqiyah is not allowed
Question 12: If Taqiyah is allowed by Islam, then why did not Imam Husain (as) resort to it? Why did he sacrifice his all on the altar of truth instead of taking refuge in taqiyah?
Answer. Taqiyah is based on the principle of opting for the lesser evil. Telling a lie is not as big a sin as destroying a life. Therefore, lie is preferable to putting oneself in danger of life.
Now, if safety of one's own life depends upon putting another believer's life in danger, then, by the same reasoning, taqiyah is not allowed, because one believer is going to die in any case. So, it is better for you to die than to cause the death of another believer.
By the same reasoning, if there is a likelihood that one's taqiyah may destroy the belief of other believers, then taqiyah is forbidden to such a person.
Take for example the case of Imam Husain (as). The character of Yazid is well known and we need not go into its details here. Such a person demands allegience from Imam Husain (as), the grandson of the Holy Prophet of Islam and symbol of Islamic values and religious uprightness. Yazid had written to his governor of Madina to demand allegiance from Imam; and, if Imam refused, then the governor was to send his head to Damascus.
So Imam Husain (as) was well aware of the consequences of his rejection of that demand. Still, he knew that if he did swear allegiance to Yazid, Muslims would think that Yazid was the rightful successor of the Holy Prophet (saw), and thus all the debaucheries of Yazid would become a part of Islam. In short, Islam would have been completely disfigured if Imam Husain (as) had accepted Yazid as the legal Khalifah of the Holy Prophet.
Thus we come to the conclusion that if someone is of such a status that if he, resorted to taqiyah, others would be misled into un‑Islamic tenets and beliefs, then the basic principle demands that he should sacrifice his life but save others from going astray. One or more lives are not as important as one or more people's Faith and spiritual deliverance.
In the end, it should be reiterated that taqiyah is not an specialty of the Shi'as. Every sect of Islam accepts the principle. Quotations from Sahih Bukhari and Sunni Commentaries of the Qur’an have been given in this article. Imam Shafi'i allowed taqiyah even from the Muslims as well as from the infidels. And all great scholars of Sunni sect, without any exception, have written that taqiyah is valid upto the Day of Judgement. Those interested. in detailed references should see `Fulk‑un‑Najut' of Maulana Ali Muhammad and Maulana Amirud‑Deen (Lahore, Pakistan) where scores of references have been given from page 89 to page 116.
The Sunni scholar, Najmuddin Tufi Hanbali writes:
"Know that the long arguments for and against taqiyah are useless …. but there is no doubt in its validity and legality. Of course, common people do not like its name (taqiyah) because it has been identified with the Shi'as. Otherwise, the whole world uses it naturally, though some call it `tolerance', others name it as `diplomacy, and some call it `common sense'. And it is proved by proofs of Shari’ah (Islam). 
Question 13: Keeping in view, all these verses of the Qur’an and the Prophet's traditions, and looking at all these historical facts in the lives of the Holy Prophet (saw), his companions and even previous Prophets as well as the Sunni scholars, how is it that the Wahhabis go on accusing the Shi'as of various ridiculous beliefs and then declaring that even if the Shia's deny such beliefs they should not be believed because they practice taqiyah?
Answer. Well, our books are readily available in Arabic, Persian, Urdu, Gujarati, Bengali, Hindi, Swahili, English and many other languages. They are on sale in Iran, Iraq, Gulf States, Lebanon, Pakistan, India, East Africa, U.K, Canada, U.S.A and other countries. There are books on theology, jurisprudence, and social, ethical and philosophical subjects. Some are meant for our children's education, others for youths and grown up people. Let the Wahhabis produce proof from our books in support of those baseless accusations. Unfortunately, they go on repeating those foolish things from their own books and think that they have vanquished the Shi'as!!
What will they say if we start writing that: "The Wahhabis believe that Shaykh Muhammad ibn `Abdul Wahhab was their prophet, and that is why they hate the Holy Prophet, Muhammad ibn `Abdullah (saw) so much and always try to distract the Muslims from showing love and respect to the Holy Prophet of Islam (saw), but they do not dare to declare this belief openly because then, they would be turned out of Mecca and Medina and would lose their power‑base."? How will they refute this allegation? What will be their defense when we will reject their words of mouth and their writings, as we will go on asserting that it was all a pack of lies just to safeguard their hold on the sanctuaries of Mecca and Medina?
 Tufi, Sharhu 'l Arba'in an‑Nawawi as quoted in Falkun‑Najat, 2nd ed. Lahore, vol. 2, p. 107.