Sahih Bukhari | Volume 7 | Hadith Number 797

Narrated by Ibn 'Umar
I heard Allah's Apostle, while he was in the state of Ihram and his hair was stuck together with gum, saying, "Labbaik, Allahumma Labbaik, Labbaik La Shanka laka Labbaik. Inn- al-Hamda Wan-Ni'mata Laka wal-Mulk, La Shanka Lak." He did not add anything to those words. (See Hadith No. 621, Vol. 2)