Most High:

“You will be called to face a people of great military might, whom you will fight unless they submit. If you obey, Allah will grant you a good reward; but if you turn away as you did before, He will punish you with a painful punishment.”

Likewise, He describes the people of Saqar as not having been among those who prayed. He also pairs denial with turning away in His words:

“Have you seen the one who forbids a servant when he prays? Have you considered whether he is rightly guided, or enjoins righteousness? Have you considered whether he denies the truth and turns away? Does he not know that Allah sees? No! If he does not desist, We will surely seize him by the forelock—a lying, sinful forelock.”

Furthermore, in the Quran, He makes brotherhood in religion conditional upon actually establishing prayer and giving zakah, just as He makes it conditional upon repentance from disbelief. When these conditions are absent, brotherhood is absent.

It is also established that the Prophet, may Allah bless him and grant him peace, said:

“The covenant between us and them is prayer; whoever abandons it has disbelieved.”

And in the Musnad:

“Whoever deliberately abandons prayer has forfeited the covenant of protection.”

Moreover, prayer is the distinguishing mark of the Muslims. Hence they are referred to by it: people say, “Those who pray have differed,” and, “Those who face the direction of prayer have differed.” Writers on Muslim doctrines speak of “The Doctrines of the Muslims and the Disagreements among Those Who Pray.” And in the Sahīh:

“Whoever prays as we pray, faces our direction of prayer, and eats the animals we slaughter is a Muslim, entitled to the same rights as us and bound by the same duties.”

There are many similar texts in the Quran and Sunnah. As for those who do not regard abandoning prayer and similar duties as disbelief, they have no argument that is not