Sahih Bukhari Volume 008, Book 077, Hadith Number 607.
Narated By Abu Musa : While we were with Allah's Apostle in a holy battle, we never went up a hill or reached its peak or went down a valley but raised our voices with Takbir. Allah's Apostle came close to us and said, "O people! Don't exert yourselves, for you do not call a deaf or an absent one, but you call the All-Listener, the All-Seer." The Prophet then said, "O 'Abdullah bin Qais! Shall I teach you a sentence which is from the treasures of Paradise? (It is): 'La haula wala quwata illa billah. (There is neither might nor power except with Allah)."