From Sahih Bukhari (Hadith 1410):
Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "If one gives in charity what equals one date-fruit from the honestly earned money and Allah accepts only the honestly earned money --Allah takes it in His right (hand) and then enlarges its reward for that person (who has given it), as anyone of you brings up his baby horse, so much so that it becomes as big as a mountain
Reference: Bukhari 1410