Chapter 12: The traveler’s takbīr (saying “Allāhu Akbar”) when ascending hills and the like; his tasbīḥ (saying “Subḥān Allāh”) when descending into valleys and similar places; and the prohibition of exaggerating by raising the voice excessively while uttering the takbīr or the like.

975 – Jābir (may Allah be pleased with him) said, “Whenever we climbed, we would pronounce the takbīr, and whenever we went down, we would pronounce the tasbīḥ.” Reported by al-Bukhārī.

976 – Ibn ʿUmar (may Allah be pleased with them both) said, “Whenever the Prophet ﷺ and his armies reached the top of a rise, they would pronounce the takbīr; and whenever they descended, they would pronounce the tasbīḥ.” Reported by Abū Dāwūd with a sound chain of transmission.

[Explanation]
Imām al-Nawawī (may Allah have mercy on him) placed this chapter in “Riyāḍ al-Ṣāliḥīn” under the heading of the etiquettes of travel and the supplications prescribed for it. Among those etiquettes is that when a person ascends an elevated place—such as a mountain, or, in our day, when an airplane rises—he pronounces the takbīr, saying “Allāhu Akbar” once, twice, or three times. When he descends, he makes the tasbīḥ, saying “Subḥān Allāh” once, twice, or three times. The rationale is that when a person rises, he sees himself in a lofty position and may begin to think highly of himself,