Volume 4 · Book 52 · Hadith 236
Narrated Jabir bin 'Abdullah: Whenever we went up a place we would say, "Allahu--Akbar (i.e. Allah is Greater)", and whenever we went down a place we would say, "Subhan Allah."
— Sahih Bukhari, Volume 4, Book 52: Fighting for the Cause of Allah (Jihaad), Hadith #236