The necessity of sincere intention and belief

مَثَلُ مَا يُنفِقُونَ فِى هَـٰذِهِ ٱلْحَيَوٰةِ ٱلدُّنْيَا كَمَثَلِ رِيحٍ فِيهَا صِرٌّ أَصَابَتْ حَرْثَ قَوْمٍ ظَلَمُوٓا۟ أَنفُسَهُمْ فَأَهْلَكَتْهُ ۚ وَمَا ظَلَمَهُمُ ٱللَّهُ وَلَـٰكِنْ أَنفُسَهُمْ يَظْلِمُونَ

The example of what they spend in this worldly life is like that of a wind containing frost which strikes the harvest of a people who have wronged themselves [i.e., sinned] and destroys it. And Allāh has not wronged them, but they wrong themselves.