On this issue, we’d like to clarify that some scholars opine that Sa`y (between the two hills of Safa and Marwah) is an essential part of Hajj rites, so if a pilgrim fails to perform Sa`y, his Hajj will be void.
According to some other scholars, it is Sunnah, while a third group holds that it is wajib (requisite), and this is the preferred view. Therefore, if a pilgrim fails to perform it, he must sacrifice an animal.
Elaborating more on this issue, we cite what Sheikh Sayyed Sabiq states in his well-known book Fiqh Us-Sunnah:
“Scholars differ concerning the legal status of Sa`y between Safa and Marwah. The views of the scholars may be classified into three:
1. According to `A’ishah, Ibn `Umar, and Jabir, Sa`y is an essential part of Hajj rites. Malik, Ash-Shafi`i, and Ahmad (according to one of his narrations) also hold a similar opinion. Thus, if a pilgrim fails to perform Sa`y, his Hajj will be void and offering a sacrifice will not be sufficient to atone for it.
2. According to Ibn `Abbas, Anas, Ibn Az-Zubayr, Ibn Sirin, and Ahmad (according to one of his narrations), Sa`y is Sunnah, and if it is not performed, there is no penalty incurred on the person neglecting it.
3. According to Abu Hanifah, At-Thawri, and Al-Hasan, Sa`y between Safa and Marwah is wajib but not fard (obligatory) for Hajj or `Umrah. Therefore, if a pilgrim fails to perform it, he must sacrifice a sheep.
The author of Al-Mughni prefers this opinion and says: “This is preferable because the argument of those who believe that it is wajib supports the absolute nature of the obligation rather than the principle that anything needed to fulfill an obligation (wajib) is also obligatory (wajib).”