Musnad Abu Ya'la al-Mawsili 109:123

Ishaq narrated to us, Affan narrated to us, Hammad bin Salamah narrated to us, from Humayd, from Abu al-Mutawakkil, from Jabir bin Abdullah: That they would not place their hands into the food until the Messenger of Allah, may Allah bless him and grant him peace, would begin.