Who are the greatest losers in respect of (their) deeds? Are the sinners included with them?

I hope you can give the tafseer (commentary) onthis passage:
"Say (O Muhammad SAW): Shall We tell you the greatest losers in
respect of (their) deeds?
Those whose efforts have been wasted in thislife while they thought
that they were acquiringgood by their deeds!
They are those who deny the Ayat (proofs, evidences, verses, lessons,
signs, revelations, etc.) of their Lord and the Meeting with Him (in
the Hereafter). So their works are in vain, and on the Day of
Resurrection, We shall not give them any weight"
[al-Kahf 18:103-105].
What I am asking for is an explanation of who are the greatest losers
inrespect of their deeds among the Muslims? Is the one who does not
follow the Messenger of Allah with regard to the command to let the
beard grow one of the greatest losers in respectof their deeds, or is
this not connected to what Allah says in this verse?
I also hope you will explain the du'aa' of the Prophet and Messenger
of Allah for forgiveness for those who shave; arethey the ones who
shavetheir beards?.
Praise be to Allaah.
Firstly:
This verse is from Soorat al-Kahf, which is a Makkan soorah (revealed
in Makkah). It was revealed concerningthe kuffaar idol-worshippers
whose devils lead them astray and made their actions seem good to
them, so they thought that they were guided and that the Muslims were
misguided. Allah, may Hebe exalted, tells us aboutthat in the verse
(interpretation of the meaning): "And verily, they (Satans / devils)
hinder them from the Path (of Allah), but they think that they are
guided aright!" [az-Zukhruf 43:37]. And He, may He be exalted, said
(interpretation of the meaning): "A group He has guided, and a group
deserved to be in error; (because) surely they took the Shayatin
(devils) as Awliya (protectors and helpers) instead of Allah, and
consider that they are guided" [al-A'raaf 7:30]. And Allah, may He be
exalted, stated that they are disbelievers when Hesaid in the same
passage(that you asked about): "They are those who deny the Ayat
(proofs, evidences, verses, lessons, signs, revelations, etc.) of
their Lord and the Meeting with Him (in the Hereafter)." [al-Kahf
18:104].
The fact that these verses were revealed concerning the mushrikeen is
something about which there can be no doubt, because this verse is
Makkan (revealed in Makkah), as we stated above. This does not mean
that it cannot include others; it also includes the Jews and
Christians, according to the wording, the meaning and the ruling. And
it includes the followers of innovation and misguidance, commensurate
with what their beliefs and actions include of misguidance and things
that are contrary to sharee'ah. So the nullification of their good
deeds – in these verses – is complete in the case of the kuffaar,
mushrikeen and apostates; as for the followers of innovation and
misguidance amongthe Muslims, their deeds are not nullified
completely; rather those that are innovated and contrary to sharee'ah
are nullified.
Ibn Katheer (may Allah have mercy on him) said:al-Bukhaari narrated
that Mus'ab said: I asked my father – i.e., Sa'd ibn Abi Waqqaas –
"Say (O Muhammad SAW): Shall We tell you the greatest losers in
respect of (their) deeds?": does thisrefer to the Harooris
(Khaarijis)? He said: No; they are the Jews and the Christians. As for
the Jews, they rejected Muhammad (blessings and peace of Allah be upon
him); as for the Christians, they disbelieved in Paradise and said
that there is no food or drink in it. The Harooris are the one who
broke Allah's Covenant after ratifying it (cf. al-Baqarah 2:29). and
Sa'd (may Allah be pleased with him) used to call them the evildoers
(al-faasiqeen).
'Ali ibn Abi Taalib, ad-Dahhaak and others said: They are the
Harooris, i.e., the Khaarijis.
What is meant by these words of 'Ali (may Allah be pleased with him)
is that this verse includes the Harooris as well as the Jews,
Christians and others; it does not mean that it was revealed
specifically concerning the former and not the latter. In fact it is
more general in meaning thanthis; this verse was revealed in Makkah,
before the message was addressed to the Jews and Christians, and
before the Khaarijis even existed. It is general in meaning and
applies to everyone whoworships Allah in any way that is not pleasing
to Him, thinking that he has got it right and that his deeds are
acceptable,when in fact he has got it wrong and his deeds are
rejected, as Allah, may He be exalted, says (interpretation of the
meaning):
"Some faces, that Day, will be humiliated (in the Hell-fire, i.e. the
faces of all disbelievers)
Labouring (hard in the worldly life by worshipping others besides
Allah), weary (in the Hereafter with humility and disgrace).
They will enter in the hot blazing Fire"
[al-Ghaashiyah 88:2-4]
"And We shall turn to whatever deeds they (disbelievers,
polytheists,sinners, etc.) did, and Weshall make such deeds
asscattered floating particles of dust"
[al-Furqaan 25:23]
"As for those who disbelieve, their deeds are like a mirage in a
desert. The thirsty one thinks it to be water, until he comes up to
it, he finds it to be nothing"
[an-Noor 24:39].
And in this verse, He says: "Say: Shall We tell you" i.e., shall We informyou
"the greatest losers in respect of (their) deeds".Then He explains who
they are and says:
"Those whose efforts have been wasted in thislife" i.e., they did
invalid deeds that were not in accordance with sharee'ah, and were not
prescribed, pleasing to Allah or acceptable.
"while they thought thatthey were acquiring good by their deeds" i.e.,
they believed that they were doing something good, and that they were
accepted and loved.
End quote from Tafseer Ibn Katheer, 5/201, 202
It is worth noting that Shaykh al-Islam Ibn Taymiyah (may Allah have
mercy on him) commented on the verses from al-Ghaashiyah – which are
mentioned above in the quotation from Ibn Katheer – and said that they
refer to the Day of Resurrection, and that the faces of the
disbelievers on that day will be humiliated, that is disgraced. But
that is not in this world. See Majmoo' al-Fataawa, 16/217-220
Thus it is known that theverse does not include the one who disobeys
Allah, may He be exalted,and shaves his beard. Rather the verses speak
about the worship of anything other than Allah, and it is known that
the verse was originally revealed about the disbelievers, and the
inclusion of the followers of innovation under that heading is done of
the basis of analogy.
Secondly:
The hadeeth of 'Abdullahibn 'Umar (may Allah be pleased with him) –
which states that the Messenger of Allah (blessings and peace of Allah
be upon him) said: "O Allaah, have mercy onthose who shaved their
heads." They said: And those who cut their hair,O Messenger of Allaah?
He said: "May Allaah have mercy on those who shaved their heads." They
said: And those who cut their hair,O Messenger of Allaah? He said:
"And those who cut their hair" (narrated by al-Bukhaari, 1640; Muslim,
1301) – has nothing to do with shaving or cutting the beard; rather it
undoubtedly has to do with exiting ihram following 'Umrah or Hajj by
shaving the hair of the head. We do not think that any Muslim would
dare to say that shaving (when exiting ihram) includes shaving the
beard. The one who says that is extremely ignorant and he should be
taught and disciplined, because he has spoken about Allah, may He be
exalted, without knowledge. If the one who said that is someone who
claims to have knowledge, then undoubtedly his saying that is a
mockery and is toying with the verses ofAllah and distorting the
words.
And Allah knows best.