قُلْ هَلْ نُنَبِّئُكُم بِالاٌّخْسَرِينَ أَعْمَـلاًالَّذِينَ ضَلَّ سَعْيُهُمْ فِى الْحَيَوةِ الدُّنْيَا وَهُمْ يَحْسَبُونَ أَنَّهُمْ يُحْسِنُونَ صُنْعًاأُوْلَـئِكَ الَّذِينَ كَفَرُواْ بِـَايَـتِ رَبِّهِمْ وَلِقَائِهِ فَحَبِطَتْ أَعْمَالُهُمْ فَلاَ نُقِيمُ لَهُمْ يَوْمَ الْقِيَـمَةِ وَزْناًذَلِكَ جَزَآؤُهُمْ جَهَنَّمُ بِمَا كَفَرُواْ وَاتَّخَذُواْ ءَايَـتِى وَرُسُلِى هُزُواًSay: Shall We tell you the greatest losers in respect of (their) deeds?Those whose efforts have been wasted in this life while they thought that they were acquiring good by their deeds.They are those who deny the Ayat of their Lord and the meeting with Him. So their works are in vain, and on the Day of Resurrection, We shall assign no weight for them.That shall be their recompense, Hell; because they disbelieved and took My Ayat and My Messengers for jest.
Al-Bukhari recorded from `Amr that Mus`ab who said:
"I asked my father (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 , 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)
Reference: Tafsir Ibn Kathir, available at qtafsir.com