Sahih Bukhari Volume 002, Book 026, Hadith Number 689.
Narated By Abu Huraira : In the year prior to the last Hajj of the Prophet when Allahs Apostle made Abu Bakr the leader of the pilgrims, the latter (Abu Bakr) sent me in the company of a group of people to make a public announcement: 'No pagan is allowed to perform Hajj after this year, and no naked person is allowed to perform Tawaf of the Kaba.' (See Hadith No. 365 Vol. 1)