Sahih Bukhari Volume 2, Book 24, Hadith 1416

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، حَدَّثَنَا أَبُو النُّعْمَانِ الْحَكَمُ ـ هُوَ ابْنُ عَبْدِ اللَّهِ الْبَصْرِيُّ ـ حَدَّثَنَا شُعْبَةُ، عَنْ سُلَيْمَانَ، عَنْ أَبِي وَائِلٍ، عَنْ أَبِي مَسْعُودٍ ـ رضى الله عنه ـ قَالَ لَمَّا نَزَلَتْ آيَةُ الصَّدَقَةِ كُنَّا نُحَامِلُ، فَجَاءَ رَجُلٌ فَتَصَدَّقَ بِشَىْءٍ كَثِيرٍ فَقَالُوا مُرَائِي‏.‏ وَجَاءَ رَجُلٌ فَتَصَدَّقَ بِصَاعٍ فَقَالُوا إِنَّ اللَّهَ لَغَنِيٌّ عَنْ صَاعِ هَذَا‏.‏ فَنَزَلَتِ ‏{‏الَّذِينَ يَلْمِزُونَ الْمُطَّوِّعِينَ مِنَ الْمُؤْمِنِينَ فِي الصَّدَقَاتِ وَالَّذِينَ لاَ يَجِدُونَ إِلاَّ جُهْدَهُمْ‏}‏ الآيَةَ‏.‏

Narrated By Abu Masud : When the verses of charity were revealed, we used to work as porters. A man came and distributed objects of charity in abundance. And they (the people) said, "He is showing off." And another man came and gave asa (a small measure of food grains); they said, "Allah is not in need of this small amount of charity." And then the Divine Inspiration came: "Those who criticize such of the believers who give in charity voluntarily and those who could not find to give in charity except what is available to them." (9.79).