Musnad Ahmad 30:1320

Zayd ibn al-Hubab narrated to us, al-Dahhak ibn Uthman narrated to me—in the year fifty-one I went out with Sufyan—he said: Bukayr ibn Abd Allah ibn al-Ashajj narrated to me, from Sulayman ibn Yasar, from Abu Hurayrah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever buys food, let him not sell it until he has taken full possession of it."