Musannaf Ibn Abi Shayba 17:1021

Narrated to us Abd al-Rahim ibn Sulayman, from Abd Allah ibn Sa’id, from his father, from a man from Aslam who is called Ibn al-Adra’, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Adopt the way of Ma'add (i.e., live a rugged life), be rough, practice archery, and walk barefoot."