Musnad Ahmad 28:73

Yazid narrated to us, Hammad ibn Salamah informed us, from Thabit al-Bunani, from Shu'ayb ibn Abdullah ibn Amr, from his father, who said: "I never saw the Messenger of Allah, may Allah bless him and grant him peace, eating while reclining at all, nor did two men walk behind him." Affan said: "His heels."