Sahih Bukhari Volume 5, Book 57, Hadith Number 46.

Narated By Anas : Allah’s Apostle ascended the (mountain) of Uhud with Abu Bakr and ‘Uthman and it shook. Allah’s Apostle said, “Be calm, O Uhud!” I think he stroked it with his foot and added, “There is none on you but a Prophet, a Siddiq and two martyrs.” (The two martyrs were Umar and Uthman) (See Hadith No. 24)