Musannaf Ibn Abi Shayba 13:1228

Abu Bakr narrated to us, he said: Abd al-Wahhab al-Thaqafi narrated to us, from Khalid, from Muhammad, that he said: If a man buys dates while they are on the palm trees, there is no harm in him selling them before he harvests them. He said: Muhammad used to see no harm in it for a time. But when they increased [their questioning] of him regarding it, he said: "Leave what makes you doubt for what does not make you doubt."