Musnad Ahmad 30:3814

Hashim narrated to us, Laith narrated to us, Sa'id al-Maqburi narrated to me, from Sa'id ibn Yasar, the brother of Abu Marthad, that he heard Abu Hurairah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "No one gives charity from what is good—and Allah does not accept except what is good—but the Most Gracious (al-Rahman), Mighty and Majestic is He, takes it with His Right Hand. Even if it is a single date, it grows for him in the palm of the Most Gracious until it becomes greater than a mountain, just as one of you raises his foal or his young camel."