Musnad Ahmad 27:1539

Ya'qub narrated to us, my father narrated to me, from Ibn Ishaq, my father Ishaq ibn Yasar narrated to me, from Abdullah ibn Qays ibn Makhramah, who said: I came from the mosque of Banu 'Amr ibn 'Awf in Quba' on a mule of mine, having prayed in it. I met Abdullah ibn Umar walking. When I saw him, I dismounted from my mule and said: "Ride, O uncle." He said: "O son of my brother, if I wanted to ride beasts, I would have found them. But I saw the Messenger of Allah, may Allah bless him and grant him peace, walking to this mosque until he would arrive and pray in it, so I love to walk to it just as I saw him walking." He said: So he refused to ride and continued on his way.