Sahih Muslim | Book 5 | Hadith Number 2211

Narrated by Abu Huraira
Abu Huraira reported Allah's Messenger (tray peace be upon him) as saying: If anyone gives as Sadaqa the equivalent of a date from that (earning) earned honestly, for Allah accepts that which is lawful, the Lord would accept it with His Right Hand, and even if it is a date, it would foster in the Hand of the lord, as one of you fosters his colt, till it becomes bigger than a mountain.