Sahih Bukhari

Narrated Abu Mas`ud: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 a Sa (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