Al-Bukhari recorded from `Amr that Mus`ab who said: "I asked my father -- meaning Sa`d bin Abi Waqqas -- about Allah's saying,
قُلْ هَلْ نُنَبِّئُكُم بِالاٌّخْسَرِينَ أَعْمَـلاً
(Say: "Shall We tell you the greatest losers in respect of (their) deeds") `Are they the Haruriyyah' He said, `No, they are the Jews and Christians. As for the Jews, they disbelieved in Muhammad ﷺ, and as for the Christians, they disbelieved in Paradise and said that there is no food or drink there, and the Haruriyyah are those who break Allah's covenant after ratifying it.' Sa`d used to call them Al-Fasiqin (the corrupt). `Ali bin Abi Talib, Ad-Dahhak and others said: "They are the Haruriyyah," so this means, that according to `Ali, may Allah be pleased with him, this Ayah includes the Haruriyyah just as it includes the Jews, the Christians and others. This does not mean that the Ayah was revealed concerning any of these groups in particular; it is more general than that, because the Ayah was revealed in Makkah, before the Qur'an addressed the Jews and Christians, and before the Khawarij existed at all. So the Ayah is general and refers to everyone who worships Allah in a way that is not acceptable, thinking that he is right in doing that and that his deeds will be accepted, but he is mistaken and his deeds will be rejected, as Allah says:
وُجُوهٌ يَوْمَئِذٍ خَـشِعَةٌ - عَامِلَةٌ نَّاصِبَةٌ - تَصْلَى نَاراً حَامِيَةً
(Some faces, that Day will be humiliated. Laboring, weary. They will enter in the hot blazing Fire.) 88:2-4
وَقَدِمْنَآ إِلَى مَا عَمِلُواْ مِنْ عَمَلٍ فَجَعَلْنَاهُ هَبَآءً مَّنثُوراً
(And We shall turn to whatever deeds they did, and We shall make such deeds as scattered floating particles of dust.) 25:23
وَالَّذِينَ كَفَرُواْ أَعْمَـلُهُمْ كَسَرَابٍ بِقِيعَةٍ يَحْسَبُهُ الظَّمْآنُ مَآءً حَتَّى إِذَا جَآءَهُ لَمْ يَجِدْهُ شَيْئاً
(As for those who disbelieved, 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) 24:39 And in this Ayah Allah says:
قُلْ هَلْ نُنَبِّئُكُم
(Say: "Shall We tell you...") meaning, `Shall We inform you;'
بِالاٌّخْسَرِينَ أَعْمَـلاً
(the greatest losers in respect of (their) deeds) Then Allah explains who they are, and says:
الَّذِينَ ضَلَّ سَعْيُهُمْ فِى الْحَيَوةِ الدُّنْيَا
(Those whose efforts have been wasted in this life) meaning, they did deeds that do not count, deeds that are not in accordance with the prescribed way that is acceptable to Allah.
وَهُمْ يَحْسَبُونَ أَنَّهُمْ يُحْسِنُونَ صُنْعًا
(while they thought that they were acquiring good by their deeds.) means, they thought that there was some basis for their deeds and that they were accepted and loved.
أُوْلَـئِكَ الَّذِينَ كَفَرُواْ بِـَايَـتِ رَبِّهِمْ وَلِقَائِهِ
(They are those who deny the Ayat of their Lord and the meeting with Him.) they denied the signs of Allah in this world, the proofs that He has established of His Oneness and of the truth of His Messengers, and they denied the Hereafter.
فَلاَ نُقِيمُ لَهُمْ يَوْمَ الْقِيَـمَةِ وَزْناً
(and on the Day of Resurrection, We shall assign no weight for them.) means, `We will not make their Balance heavy because it is empty of any goodness.' Al-Bukhari recorded that Abu Hurayrah said that the Messenger of Allah ﷺ said:
«إِنَّهُ لَيَأْتِي الرَّجُلُ الْعَظِيمُ السَّمِينُ يَوْمَ الْقِيَامَةِ لَا يَزِنُ عِنْدَ اللهِ جَنَاحَ بَعُوضَةٍ وَقَالَ: اقْرَءُوا إِنْ شِئْتُمْ:
فَلاَ نُقِيمُ لَهُمْ يَوْمَ الْقِيَـمَةِ وَزْناً
(A huge fat man will come forward on the Day of Resurrection and he will weigh no more than the wing of a gnat to Allah. Recite, if you wish:) (and on the Day of Resurrection, We shall assign no weight for them) It was also recorded by Muslim.
ذَلِكَ جَزَآؤُهُمْ جَهَنَّمُ بِمَا كَفَرُواْ
(That shall be their recompense, Hell; because they disbelieved) means, `We will punish them with that because of their disbelief and because they took the signs and Messengers of Allah ﷺ as a joke, mocking them and disbelieving them in the worst way.'