وعن ابن عمر رضي الله عنهما
قال: كان النبي صلى الله عليه وسلم وجيوشه إذا علو الثنايا كبروا، وإذا هبطوا سبحوا
Whenever the Prophet (sallallahu alayhi wa sallam) and his army ascended a height, they would proclaim: “Allahu Akbar (Allah is Greatest),” and when they climbed down, they would proclaim: “Subhan Allah (Allah is free from imperfection).”.
Riyad as-Salihin 976, Book 8, The Book of Etiquette of Traveling, Hadith 21. 1 min read