Sahih Bukhari
Sahih Bukhari Volume 002, Book 026, Hadith Number 590.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 26. Pilgrimmage (Hajj)
Narated By Ibn 'Umar : I saw that Allah's Apostle used to ride on his Mount at Dhul Hulaifa and used to start saying, "Labbaik" when the Mount stood upright.