Musnad Ahmad 27:1338

Muhammad ibn Ubayd narrated to us, Ubayd Allah narrated to us, from Nafi’, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever buys date palms that have been pollinated, then their fruit belongs to the one who pollinated them, unless the one who bought them stipulates [otherwise]."