Sahih al-Bukhari 4668
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
The Statement of Allah "Those who defame such of the believers who give charity (in Allah's Cause) voluntarily..." (V.9:79)
Narrated Abu Mas`ud: When we were ordered to give alms, we began to work as porters (to earn something we could give in charity). Abu `Aqil came with one half of a Sa` (special measure for food grains) and another person brought more than he did. So the hypocrites said, "Allah is not in need of the alms of this (i.e. Abu `Aqil); and this other person did not give alms but for showing off." Then Allah revealed:-- 'Those who criticize such of the Believers who give charity voluntarily and those who could not find to give in charity except what is available to them.' (9:79)