What is the ruling on one who deems permissible reviling, and the lack of tranquility in prayer, and the lack of ritual purity in prayer, and abandoning the first Tashahhud? And are these among the matters known by necessity to be part of the religion?

The forbidden acts, the allowance of which constitutes disbelief, are those whose prohibition has been unanimously agreed upon and whose ruling has become manifest among Muslims, such that there is no room for interpretation or doubt. That which is known by necessity in religion is a definitive matter about which one finds no slightest doubt in their heart, because it is so evident that both commoners and specialists are aware of it. The ruling on declaring a person who deems a forbidden act permissible to be a disbeliever varies according to time and place. What is evident and well-known in one time or place might be obscure in others.

As for reviling: If it is reviling and cursing people, then deeming it permissible is disbelief if the reviling is by the consensus of people and the knowledge of its prohibition has become widespread among them. If it is reviling Allah Almighty or His Messenger, peace and blessings be upon him, then this is disbelief, outwardly and inwardly, whether the reviler knows that reviling is disbelief or is ignorant, and whether they deem it permissible or not. If it is reviling the noble Companions, some of it leads to the doer being declared a disbeliever, whether they deem it permissible or not, and some of it leads to being declared a fasiq (transgressor).

As for ṭuma’nīnah (tranquility) in prayer: Its omission is not something known by necessity in religion; therefore, one who deems its omission permissible does not commit an act of disbelief.

As for purity in prayer: If what is meant is ritual purity (ghusl and wudu), then deeming prayer permissible without it is disbelief, and no excuse is accepted from one who does so in a land where the rulings of Islam are manifest. If what is meant is purity from impurities (khabath), this is not something that has been agreed upon, so one who deems it permissible is not ruled to be a disbeliever.

As for the first tashahhud: It is not something known by necessity in religion, so one who deems prayer permissible without it does not commit an act of disbelief.