Riyad as-Salihin 976
Ibn 'Umar (May Allah be pleased with them) reported:
Whenever the Prophet (ﷺ) 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)." [Abu Dawud] .
وعن ابن عمر رضي الله عنهما قال‏:‏ كان النبي صلى الله عليه وسلم وجيوشه إذا علو الثنايا كبروا، وإذا هبطوا سبحوا‏.‏ ‏(‏‏(‏رواه أبو داود بإسناد صحيح‏.‏