Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.088.

Section : Climbing the Safa Mountain.

Climbing on op of Safa or Marwah is not a necessary condition for Sa’i, but one must walk back and forth the full distance between these two points. In case any part of this distance is left un-traversed the Sa’i will remain incomplete.