Musnad Ahmad 30:2300

Qutaybah narrated to us, Bakr bin Mudar narrated to us, from Ibn ‘Ajlan, that Sa‘id bin Yasar Abu al-Hubab informed him, from Abu Hurayrah, that the Messenger of Allah (ﷺ) said: "There is no believing servant who gives charity from what is pure—and Allah does not accept anything except what is pure, and nothing ascends to the heaven except what is pure—but that he places it in the hand of the Most Merciful—or in the palm of the Most Merciful—so He nurtures it for him just as one of you nurtures his foal—or his young camel—until a single date becomes like a great mountain."