"Taqiyya is an obligatory duty (farida wajiba) upon us under the governance of the oppressors, thus whoever abandons it has opposed the religion of the Imamiyyah and has separated from it.As-Sadiq (as) said, “Even if I said ‘the one who abandons taqiyya is as the one who abandons salat,’ I would be speaking the truth.”Taqiyya is in all things, until it reaches bloodshed. If it reaches bloodshed then there is no taqiyya. Allah, sublime be His name, has given validity to the appearance of friendship (muwalah) to the deniers (kafirin) in the state of taqiyya. He, `azza wa jalla, has said, “The believers do not take the unbelievers as awliya instead of the believers, then whoever does that has nothing from Allah, except if you have a fear of them.”It is related from as-Sadiq (as) that he was asked about the saying of Allah, `azza wa jalla, “Verily the most noble of you with Allah is the most fearing”. He said “The one from you who most practices taqiyya.”He (as) said, “Mix with the people on the outside, and oppose them on the inside, so long as the affair is a longing.”He (as) said, “Allah have mercy on a command we urge the people towards and it has not made us to be hated by them.”He (as) said, “Visit their sick, attend their funerals, and pray in their masaajid.”He (as) said, “One who prays in the first row with them is as though he had prayed in the first row with the Messenger of Allah (sawas).”He said, “Ostentation (riya’) with the hypocrite in his house is worship, and with the believer, is shirk.”Taqiyya is obligatory; it is not allowed to abandon it until the Qa’im (as) comes forth. Whoso abandons it has entered in the interdiction of Allah, `azza wa jalla, and the interdiction of His Messenger and the Imams, the blessings of Allah be upon them all. "
(Kitab al-Hidaya Shaykh Saduq)