Musnad Ahmad 30:516

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Ayyub, from al-Qasim ibn Muhammad, from Abu Hurayrah, who said: The Messenger of Allah (ﷺ) said: "Indeed, when the servant gives charity from what is pure, Allah accepts it from him and takes it with His right hand, and He nurtures it just as one of you nurtures his foal or his young camel. And indeed, a man may give a morsel of food in charity, and it grows in the hand of Allah—or he said: in the palm of Allah—until it becomes like the mountain. So, give charity."