Jaabir (radhi-yAllaahu 'anhu) said: While ascending, we would say:
اَللّٰهُ أَكْبَرُ
Allah is the Most Great
Allaahu 'Akbar
And when we descended we would say:
سُبْحَانَ اللّٰهِ
Glory is to Allah.
Subhaanallaah