Musnad Ahmad 27:537

'Abd al-Wahhab ibn 'Abd al-Majid al-Thaqafi narrated to us, from Ayyub, from Nafi', from Ibn 'Umar, who said: "I have not approached the Corner (the Black Stone) since I saw the Messenger of Allah, peace and blessings of Allah be upon him, touch it—neither in times of hardship nor in times of ease—except that I have touched it."