Musnad Ahmad 27:171

Yahya narrated to us, from Ubayd Allah, Nafi’ informed me, from Ibn Umar: "That he used to perform *ramal* (brisk walking) for three [circuits] and walk for four, and he claimed that the Messenger of Allah, peace and blessings of Allah be upon him, used to do that." And he used to walk between the two corners. He said: "He only used to walk between them so that it would be easier for him to touch them."