Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2212
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: No one gives Sadaqa of a date out of his honest earning, but Allah accepts it with His Right Hand, and then fosters it as one of you fosters the colt or a young she-camel, till it becomes like a mountain or even greater.