On the authority of Jābir (may Allah be pleased with him), who said: "When we ascended we would say 'Allāhu Akbar' (God is the greatest), and when we descended we would say 'Subḥān Allāh' (glory be to Allah)." Narrated by al-Bukhārī.
١٧١ - باب تكبير المسافر إذا صعد الثنايا وشبهها، وتسبيحه إذا هبط الأودية ونحوها، والنهي عن المبالغة برفع الصوت بالتكبير ونحوه
On the authority of Jābir (may Allah be pleased with him), who said: "When we ascended we would say 'Allāhu Akbar' (God is the greatest), and when we descended we would say 'Subḥān Allāh' (glory be to Allah)." Narrated by al-Bukhārī.
On the authority of Ibn ʿUmar (may Allah be pleased with them both), who said: The Prophet (peace and blessings be upon him) and his armies, when they ascended the mountain passes, would say "Allāhu Akbar", and when they descended they would say "Subḥān Allāh". Narrated by Abū Dāwūd with a sound chain.
On his authority (Ibn ʿUmar), who said: When the Prophet (peace and blessings be upon him) returned from Ḥajj or ʿUmrah, every time he rose up onto a mountain pass or an elevated tract of land he would say "Allāhu Akbar" three times, then say: "There is no deity but Allah alone, with no partner; to Him belongs the dominion and to Him belongs all praise, and He has power over all things. We return, repentant, worshipping, prostrating, praising our Lord. Allah has fulfilled His promise, granted victory to His servant, and alone defeated the confederates." Agreed upon (al-Bukhārī and Muslim). In a narration of Muslim: when he returned from the armies, the raiding parties, the Ḥajj or the ʿUmrah. His words "awfā" mean: he rose up; and his words "fadfad" — it is with a fatḥah on the two fāʾs, with an undotted dāl between them bearing a sukūn, and another dāl at its end, and it means: "the rugged, elevated portion of the land."
On the authority of Abū Hurayrah (may Allah be pleased with him): A man said: "O Messenger of Allah, I intend to travel, so advise me." He said: "Hold fast to God-consciousness (taqwā) of Allah, and to saying 'Allāhu Akbar' upon every elevated place." When the man turned to leave, he said: "O Allah, fold up the distance for him, and make the journey easy for him." Narrated by al-Tirmidhī, who said: "A good ḥadīth."
On the authority of Abū Mūsā al-Ashʿarī (may Allah be pleased with him), who said: We were with the Prophet (peace and blessings be upon him) on a journey, and whenever we climbed up to a valley we would say "Lā ilāha illā Allāh" and "Allāhu Akbar", and our voices rose high. The Prophet (peace and blessings be upon him) said: "O people, go easy on yourselves, for you are not calling upon one who is deaf or absent. Indeed He is with you; indeed He is All-Hearing, Ever-Near." Agreed upon (al-Bukhārī and Muslim). "Irbaʿū" — with a fatḥah on the single-dotted bāʾ — means: be gentle with yourselves.