It is narrated from Sayyiduna Jabir (may Allah be pleased with him). He said: When we ascended to a height, we would say Allahu Akbar, and when we descended, we would say Subhan Allah.
Hadith Referenceسنن دارمي / من كتاب الاستئذان / 2709
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح وأبو زبيد هو: عبثر بن القاسم، [مكتبه الشامله نمبر: 2716]
Hadith Takhrijاس حدیث کی سند صحیح ہے۔ دیکھئے: [بخاري 2993، 2994] ، [ابن خزيمه 2562] و [أحمد بسند ضعيف 333/3] ۔ اور ابوزبید کا نام عبثر بن القاسم ہے۔
Brief Explanation
(Commentary on Hadith 2708)
The statement of any Companion that "we used to do such-and-such" holds the status of being marfu‘ (attributed to the Prophet sallallahu alayhi wa sallam). Therefore, saying "Allahu Akbar" while ascending and "Subhan Allah" while descending is established.