رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 976
The Book of Etiquette of Traveling
Glorification of Allah by a Traveler while Ascending and Descending
وَعَنْ اِبْنِ عُمَرَ رَضِيَ اَللَّهُ عَنْهُمَا قَالَ: كَانَ اَلنَّبِيُّ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ وجيوشه إذا علو الثَّنَايَا كَبَّرُوا، وَإِذَا هَبَطُوا سَبَّحُوا. ((رَوَاهُ أَبُو دَاوُدَ بِإِسْنَادٍ صَحِيح.
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].
Riyad as-Salihin, 976