Do not Make your Charity worthless by Injury.

Surah Al-Baqara, Verse 264:
يَا أَيُّهَا الَّذِينَ آمَنُوا لَا تُبْطِلُوا صَدَقَاتِكُم بِالْمَنِّ وَالْأَذَىٰ كَالَّذِي يُنفِقُ مَالَهُ رِئَاءَ النَّاسِ وَلَا يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الْآخِرِ فَمَثَلُهُ كَمَثَلِ صَفْوَانٍ عَلَيْهِ تُرَابٌ فَأَصَابَهُ وَابِلٌ فَتَرَكَهُ صَلْدًا لَّا يَقْدِرُونَ عَلَىٰ شَيْءٍ مِّمَّا كَسَبُوا وَاللَّهُ لَا يَهْدِي الْقَوْمَ الْكَافِرِينَ
O you who believe! Do not render in vain your Sadaqah (charity) by reminders of your generosity or by injury, like him who spends his wealth to be seen of men, and he does not believe in Allah, nor in the Last Day. His likeness is the likeness of a smooth rock on which is a little dust; on it falls heavy rain which leaves it bare. They are not able to do anything with what they have earned. And Allah does not guide the disbelieving people.

Explanation of the Ayah(verse) by ibn Kathir:

This Ayah means that heavy rain left the safwan(rock) completely barren of dust. Such is the case with Allah's action regarding the work of those who show off, as their deeds are bound to vanish and disappear even though people think that these deeds are as painful as specks of dust.

(Tafsir Ibn Kathir)