Tawheed (Monotheism) in the Holy Quran

(217) They ask you about the sacred month - about fighting therein. Say, "Fighting therein is great [sin], but averting [people] from the way of Allah and disbelief in Him and [preventing access to] al-Masjid al-Haram and the expulsion of its people therefrom are greater [evil] in the sight of Allah. And fitnah is greater than killing." And they will continue to fight you until they turn you back from your religion if they are able. And whoever of you reverts from his religion [to disbelief] and dies while he is a disbeliever - for those, their deeds have become worthless in this world and the Hereafter, and those are the companions of the Fire, they will abide therein eternally.

(137) Indeed, those who have believed then disbelieved, then believed, then disbelieved, and then increased in disbelief - never will Allah forgive them, nor will He guide them to a way.

(54) O you who have believed, whoever of you should revert from his religion - Allah will bring forth [in place of them] a people He will love and who will love Him [who are] humble toward the believers, powerful against the disbelievers; they strive in the cause of Allah and do not fear the blame of a critic. That is the favor of Allah; He bestows it upon whom He wills. And Allah is all-Encompassing and Knowing.

(29) And they say, "There is none but our worldly life, and we will not be resurrected."

(7) Indeed, those who do not expect the meeting with Us and are satisfied with the life of this world and feel secure therein and those who are heedless of Our signs

(15) And when Our verses are recited to them as clear evidences, those who do not expect the meeting with Us say, "Bring us a Qur'an other than this or change it." Say, [O Muhammad], "It is not for me to change it on my own accord. I only follow what is revealed to me. Indeed I fear, if I should disobey my Lord, the punishment of a tremendous Day."

(11) And when it is said to them, "Do not cause corruption on the earth," they say, "We are but reformers."

(12) Unquestionably, it is they who are the corrupters, but they perceive [it] not.

(26) Indeed, Allah is not timid to present an example - that of a mosquito or what is smaller than it. And those who have believed know that it is the truth from their Lord. But as for those who disbelieve, they say, "What did Allah intend by this as an example?" He misleads many thereby and guides many thereby. And He misleads not except the defiantly disobedient,