There are certain conditions necessary for Sa`i to be considered valid. It should be performed after Tawaf, in seven rounds, in the mas`a (the path between Safa and Marwah), and it must begin from Safa and end at Marwah.
Elaborating more on these conditions, we cite what Sheikh Sayyed Sabiq states in his well-known book Fiqh As-Sunnah:
For Sa`i to be valid and acceptable, it must meet the following conditions:
1- It should be performed after Tawaf.
2- It must be performed in seven rounds.
3- It must begin from Safa and end at Marwah.
4- It must be performed in the mas`a, the path between Safa and Marwah, because the Prophet (peace and blessings be upon him) did so, and moreover, he explicitly told us: “Take your (religious) rites from me.” Therefore, a Sa`i performed without performing Tawaf prior to it, or one that starts from Marwah and ends at Safa, or is performed in a place other than the specified area (between Safa and Marwah), is void. (The Hanafi school holds that Sa`i after Tawaf and beginning it at Safa and ending it at Marwah, are two essential conditions for the validity of Hajj . Thus, if someone made a Sa`i before making Tawaf, or begins his Sa`i at Marwah, and ends it at Safa, his Sa`i is valid, but he is required to slaughter an animal).