Riyad as-SalihinChapter 7Hadith 297
Full Sharh — Riyad as-Salihin 297
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.
English Translation
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).".
Source
Riyad as-Salihin(رياض الصالحين)
The Book of Etiquette of Traveling
Hadith Number
297