Musnad Abu Ya'la al-Mawsili 51:12

Abu Sa'id narrated to us, 'Abdullah bin Dawud narrated to us, from Fitr, from his father, from 'Amr bin Hurayth: That the Messenger of Allah (may Allah bless him and grant him peace) passed by 'Abdullah bin Ja'far while he was selling with the youths or the boys. He said: "O Allah, bless him in his sale," or he said: "in his transaction."