Musnad Ahmad 25:1552

Muhammad ibn Abi ‘Adi narrated to us, from Ibn ‘Awn, from Muhammad, from Ibn ‘Abbas: "We traveled with the Messenger of Allah, may Allah bless him and grant him peace, between Makkah and Madinah, fearing none but Allah, the Almighty and Majestic, and we would pray two rak'ahs."