Musnad Ahmad 337:1

Waki' narrated to us, he said: Usamah bin Zaid narrated to us, from Al-Muttalib bin Abdullah bin Hantab, from Khallad bin As-Sa'ib, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever plants a crop, and birds or creatures eat from it, it will be a charity for him."