Those who say that the one who does not pray is a kaafir and those who say that he is not a kaafir both claim that there is consensus on their point of view; how are we to understand the claim of consensus on both their parts?

If the
one who does not pray does not do it because he denies that it is
obligatory, even though he is aware that Allah has commanded that prayer be
established, then he is a kaafir and an apostate according to the consensus
of the ummah. 

If a
person does not pray because he denies that it is obligatory out of
ignorance on his part that it is obligatory, such as one who is new in
Islam, he is not deemed to be a kaafir, but he is to be taught and
instructed to pray. 

Ibn
‘Abd al-Barr (may Allah have mercy on him) said: 

The
Muslims are unanimously agreed that the one who denies that prayer is
obligatory is a kaafir who is to be executed if he does not repent from that
kufr. However they differed concerning the one who affirms that it is
obligatory but deliberately does not do it even though he is able to.

End
quote from al-Istidhkaar, 2/149 

Ibn
Qudaamah (may Allah have mercy on him) said: 

The
one who does not pray must either deny that it is obligatory or not deny
that this is the case. If he denies that it is obligatory, he must be
examined further. If he is unaware of that, then he is one of those who are
ignorant of that, such as one who is new in Islam or who grew up in the
wilderness. He is to be informed and taught that it is obligatory, and he is
not to be deemed a disbeliever, because he is excused. If he is not one of
those who were unaware of that, such as one of those who grew up among the
Muslims in Muslim regions and cities, then he is not to be excused and his
claim of having been ignorant is not to be accepted from him, and he is to
be deemed a disbeliever, because the evidence for it being obligatory is
clear from the Qur’an and Sunnah, and the Muslims offer the prayer
constantly, so in this case it is basically obvious that it is obligatory,
and he is only denying it because he disbelieves in Allah, may He be
exalted, and in His Messenger and the consensus of the ummah. This person
has become an apostate from Islam and is subject to the same ruling as all
other apostates: he is to be asked to repent and to be executed if he does
not repent. I do not know if any difference of opinion concerning this
matter.

End
quote from al-Mughni, 2/156 

The
one who does not pray out of heedlessness concerning it and out of a lack of
regard for its importance is the one concerning whom the scholars differed.
Some of them ruled that he is a disbeliever and others ruled that he is not
a disbeliever; some ruled that he is a disbeliever if he does not pray at
all, but if he prays sometimes and does not pray at other times, then he is
not to be deemed a disbeliever. 

It
says in al-Mawsoo‘ah al-Fiqhiyyah (27/53-54): 

The
Maalikis and Shaafa‘is are of the view that the one who does not pray out of
carelessness and laziness, not because he denies that it is obligatory, is
to be executed as a hadd punishment, i.e., after death he comes under the
same ruling as other Muslims, so he is to be washed (ghusl), the funeral
prayer is to be offered for him and he is to be buried with the Muslims. 

The
Hanbalis are of the view that the one who does not pray out of laziness is
to be advised to do it and he should be told: If you pray, all well and
good, otherwise we will execute you. Then if he prays, all well and good,
otherwise he must be executed. But he is not to be executed until he has
been detained for three days and called at the time of every prayer. Then if
he prays, all well and good, otherwise he is to be executed as a hadd
punishment or, it was said, he is to be executed for his disbelief, which
means that he is not to be washed, the funeral prayer is not to be offered
for him, and he is not to be buried in the Muslim graveyard. However he is
not to be enslaved and his family and children are not to be taken captive,
like other apostates. End quote. 

Ibn
‘Uthaymeen (may Allah have mercy on him) said: 

What
appears to me to be the case is that he does not become a disbeliever unless
he does not pray altogether, i.e., he never prays; as for the one who prays
sometimes, he is not a disbeliever.

End
quote from Majmoo‘ Fataawa Ibn ‘Uthaymeen, 12/55 

See
also the answer to questions no. 5208 and
83165

More
than one of the scholars have stated that there was consensus that the one
who does not pray becomes a disbeliever. Ishaaq ibn Raahawayh said: This is
the opinion of the scholars from the time of the Prophet (blessings and
peace of Allah be upon him) until our present time.

End
quote from al-Istidhkaar, 2/150 

They
quoted as evidence the apparent meaning of the texts that described him as a
disbeliever, and the words of ‘Abdullah ibn Shaqeeq al-‘Uqayli: The
Companions of Muhammad (blessings and peace of Allah be upon him) did not
think that failing to do any action constituted disbelief except in the case
of prayer.

Narrated by at-Tirmidhi (2622); classed as saheeh by al-Albaani in Saheeh
at-Tirmidhi 

See
also the answer to question no. 9400 

Those
who differed from them narrated that there was consensus that he does not
become a disbeliever. They said: 

That
is the consensus of the Muslims. We do not know of anyone, during any
period, among those who did not pray, who was not washed or the funeral
prayer was not offered for him or he was not buried in the Muslim graveyard,
or his heirs were prevented from inheriting from him or he was prevented
from inheriting from his Muslim relatives, if they died, and there was no
separation between spouses if one of them did not pray, even though there
were many such people. If (the one who does not pray) was indeed a
disbeliever, then all of these rulings would have been applied. We do not
know of any difference of opinion among the Muslims concerning the fact that
the one who does not pray is obliged to make them up; if he was an apostate,
he would not be obliged to make up his prayers and fasts (after repenting).
With regard to the hadeeths which say that he is a disbeliever, they are to
be understood as highlighting the seriousness of failing to pray, and
likening the one who does that to the disbelievers; they are not to be
understood literally. This is like the hadeeth of the Prophet (blessings and
peace of Allah be upon him), “Reviling a Muslim is evildoing and fighting
him is disbelief (kufr)” and “The one who drinks alcohol is like one who
worships an idol” and so on. What is meant in these hadeeths is to issue a
stern warning.

See
al-Mughni, 2/157 

Such
matters may be a case of ijtihaad on both sides. The first group thought
that the words of ‘Abdullah ibn Shaqeeq quoted above appeared to mean that
there was consensus among the Sahaabah that the one who does not pray is a
disbeliever, therefore they narrated that there was consensus. 

The
other group thought that the actions of Muslims during all eras – namely
washing the one who did not pray, offering the funeral prayer for him,
burying him in the Muslim graveyard, and so on – were an indication of
consensus among the Muslims that he (the one who does not pray) is not a
disbeliever. And they thought that the hadeeths which appear to mean that he
is a disbeliever were intended to highlight the seriousness of not praying
and to warn against it. This includes the report of ‘Abdullah ibn Shaqeeq. 

The
matter is one concerning which there is a difference of opinion; as the
scholars differed concerning the texts and the understanding thereof, they
also differed concerning what seemed to indicate that there was consensus.
It cannot be said that if one group quoted shar‘i texts as evidence, how can
the other group have been unaware of those texts?, because the texts were
not hidden from them, but they differed in their understanding of them and
the rulings they pointed to. Something similar may be said with regard to
the matter of consensus; those who said that the one who does not pray is
not a disbeliever are not denying these hadeeths or rejecting the words of
Ibn Shaqeeq quoted above, but they think that these texts – even though the
word kufr (disbelief) was used to describe the one who does not pray – do
not mean that he is a disbeliever in the sense of disbelief that puts him
beyond the pale of Islam. Hence this issue is one of the issues in which
there a difference of opinion is acceptable. 

The
first group narrated that there was consensus based on the apparent meaning
of the texts, of which no one disputes the soundness, and on the words of
Ibn Shaqeeq and Ishaaq ibn Raahawayh, and so on. 

The
second group narrated that there was consensus on the basis of what they saw
of the actions of the ummah in all times and places. 

If
either of these two groups had been convinced of the other’s claim that
there was consensus, and had agreed that it was well-founded, then they
would have gone along with them. But the problem in this case was that
neither group accepted the evidence of the other. 

And
Allah knows best.