Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.087.

For Sa’i to be valid and acceptable, it must meet the following conditions:

1. Should be performed after tawaf.

2. Must be performed in seven rounds.

3. Must begin from Safa and end at Marwah.

4. Must be performed in Al-Mas’a, the path between Safa and Marwah, because the Prophet (peace 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)