Musnad Ahmad 32:1545

Ya'qub narrated to us, my father narrated to us, from Muhammad ibn Ishaq, who said: Humayd al-Tawil narrated to me, from Anas ibn Malik, who said: "We used to pray the Friday prayer with the Messenger of Allah, may Allah bless him and grant him peace, then we would return to the midday rest (qaylulah) and take a nap."