Musnad Ahmad 30:2310

Qutaybah ibn Sa'id narrated to us, he said: Ya'qub—meaning ibn 'Abd al-Rahman—narrated to us, from Suhayl ibn Abi Salih, from his father, from Abu Hurayrah, that the Messenger of Allah (ﷺ) said: "No one gives in charity a date from pure earnings, but that Allah takes it with His right hand, and He nurtures it for him just as one of you nurtures his foal—or his young camel—until it becomes like the mountain, or even greater."