Musnad Ahmad 28:513

Ali ibn Ishaq narrated to us, Abdullah—meaning Ibn al-Mubarak—informed us, Usamah ibn Zayd narrated to me, Amr ibn Shu'ayb narrated to me, from his father, from Abdullah ibn Amr, who said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade buying and selling in the mosque."