Dua while ascending or descending 

Jaabir (radhi-yAllaahu 'anhu) said: While ascending, we would say:

اللّٰهُ أَكْبَرُ

Allah is the Most Great

Allaahu 'Akbar 

اللّٰهُ أَكْبَرُ

Allah is the Most Great

And when we descended we would say:

سُبْحَانَ اللّٰهِ

Glory is to Allah.

Subhaanallaah 

سُبْحَانَ اللّٰهِ

Glory is to Allah

 

Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 6/135.