Musnad Ishaq

Benefits:
By "Abtah" is meant the valley between Safa and Marwah, as is mentioned in the narration of Sayyiduna Jabir radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam ascended Safa, and after performing the specific acts there, when he descended to go towards Marwah and both his feet entered the low part of the valley, he ran until he ascended from the low ground. (Muslim, no. 1218)

Nowadays, the place of Sa'i has been leveled and a paved path has been made, but in the blessed era of the Messenger of Allah sallallahu alayhi wa sallam, the boundaries of the area that was low have been marked with green signs, and these signs are called "Milayn Akhdarayn." One should run between them, and in the rest of the area, one should walk at a normal pace. However, if a person is ill or weak and cannot run, then he may perform Sa'i at a normal pace as well. As narrated from Sayyiduna Abdullah bin Umar radi Allahu anhu, he said: If I run between Safa and Marwah, (it is correct because) I saw the Messenger of Allah sallallahu alayhi wa sallam running at this place, and if I walk (at a normal pace), (that too is correct because) I saw the Messenger of Allah sallallahu alayhi wa sallam walking as well, and I am an old man of advanced age (so running feels difficult). (Sunan Ibn Majah, no. 2988)