Sahih Bukhari, Chapter: Pilgrimage (Hajj)

Ibn Umar said, "I have never missed the touching of these two stones of Kaaba (the Black Stone and the Yemenite Corner) both in the presence and the absence of crowds, since I saw the Prophet touching them." I asked Nafi': "Did Ibn 'Umar use to walk between the two Corners?" Nafi' replied, "He used to walk in order that it might be easy for him to touch it (the Corner Stone)."