In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Allaah [The Most High] said:
مَّثَلُ ٱلَّذِينَ كَفَرُواْ بِرَبِّهِمۡۖ أَعۡمَـٰلُهُمۡ كَرَمَادٍ ٱشۡتَدَّتۡ بِهِ ٱلرِّيحُ فِى يَوۡمٍ عَاصِفٍ۬ۖ لَّا يَقۡدِرُونَ مِمَّا ڪَسَبُواْ عَلَىٰ شَىۡءٍ۬ۚ ذَٲلِكَ هُوَ ٱلضَّلَـٰلُ ٱلۡبَعِيدُ
The parable of those who disbelieve in their Lord is that their works are as ashes, on which the wind blows furiously on a stormy day, they shall not be able to get aught of what they have earned. That is the straying, far away (from the Right Path). [14:18]
There is a wonderful underlying reason in likening them [i.e. those deeds] to ashes – due the similarity between their deeds and the disappearance of the ashes found in burning fire, the similarity between the original nature of the ashes and their deeds. Deeds carried out for other than the sake of Allaah are a cause of destruction and as a result of that the fire will be kindled for those who performed them. Allaah [Glorified Be He] will punish them as a result of their false deeds, just as He will bring about bliss and comfort for those people whose deeds were in conformity with His command and carried out for His Sake. Their deeds, the things they worshipped besides Allaah and themselves are fuel for the fire.
[Source: I’laam Al-Muwaqqi-een. 1/223-224. Abridged and slightly paraphrased]