All the schools agree that sa’y follows the tawaf, or its rak'atayn for those who consider them wajib. So also they agree that one who performs sa’y before tawaf should revert and perform his tawaf first and then the sa’y. I haven't come across any opinion holding that the sa’y must immediately follow the tawaf (muwalat).1
According to the book Fiqh al‑Sunnah, it is mustahabb to ascend the hills of Safa and Marwah, and, facing the Holy Ka'bah, to pray to God for some religious or secular matter. It is well known that the Prophet (s), going out from Bab al‑Safa until he could see the Ka'bah. Facing it, he thrice declared the Unity of God and magnified Him; then praising God he said:
لا إله إلا الله وحده لا شريك له، له الملك، والله الحمد، يحيي ويمت، وهو على كل شيءٍ قدير، لا إله إلا الله وحده، أنجز وعده، ونصر عبده، وهزم الأحزاب وحده
There is no god except Allah. He is One, and has no partner. To Him belongs the Kingdom and the Praise. He gives life and makes to die and He is powerful over every thing. There is no god except Allah. He is One. He has fulfilled His promise and granted victory to His slave, vanquishing all the parties (of the infidels). He is One.
The mustahabbat of sa’y according to the Imamiyyah book al-Jawahir are the following: to draw one's hand on the Black Stone; to drink from the water of Zamzam and to sprinkle it on oneself; to leave [al‑Masjid al‑Haram] through the door facing the Black Stone; to ascend the Safa; to face al‑Rukn al‑`Iraqi; to praise God (hamd) and magnify Him (takbir); to prolong one's stay al‑Safa; and, after seven takbirs, to say three times:
لا إله إلا الله وحده، لا شريك له، له الملك، والله، الحمد، يحيي ويميت، وهوحيٌ لا يموت، بيده الخير، وهو على كل شيءٍ قدير.
After this he recites the prayer recommended by tradition (al‑du`a' al‑ma'thur).
As can be seen from the above, there is no divergence in this matter between the Shi`ah and the Sunni schools, except for some difference of expressions used. Also, I have not come across any jurist who regards taharah (from hadath and khabath) as obligatory for sa`y; most of the schools have expressly stated its being only mustahabb and the same is true (except for the Shafi'i) of the drawing of the hand (istilam) on the Black Stone before leaving for sa’y.
Also, all the schools are explicit about the istihbab of covering the distance between `the Milayn' (an expression used by the Hanafis and Malikis) or `the intervening distance' (wasat al‑masafah, an expression used by Shafi'is) or `between the Minaret and the Alley of the Pharmacists' (as Imamiyyah say) with a fast pace (harwalah). 2 Without doubt, an informed guide is necessary to enable the pilgrims to recognize the points designated as `Milayn' or `the Alley of the Pharmacists' (Zuqaq al‑`Attarin), or `the Minaret'.
Although there is agreement between the schools about the necessity of sa’y, they disagree about its being an essential part (rukn) of the rites of Hajj. According to the Imami, Shafi`i, and Maliki schools, it is a rukn; according to Abu Hanifah, it is not a rukn, though a wajib. Two different traditions are narrated from Ahmad ibn Hanbal. (al‑Tadhkirah, Fiqh al‑Sunnah)
All are agreed on the number of ashwat (sing. shawt) being seven, and that the performer of sa’y (i.e. sa’i) should begin at Safa going towards Marwah, and return again to Safa,3 covering this distance seven times. Thus the pilgrim makes four ashwat going from Safa to Marwah and three ashwat while returning from Marwah to Safa, beginning his first shawt from Safa and finishing the seventh at Marwah.
The schools disagree as to the permissibility of making the sa’y on a mount in spite of the ability to walk, and all of them, with the exception of the Hanbalis, permit it regardless of whether one can walk or not. The Hanbalis say that it is permissible only for one who cannot walk.
I have not come across any opinion regarding continuity (muwalat) between the ashwat as wajib4, with the exception of the Hanbalis, who, as also mentioned by the author of al‑Fiqh `ala al‑madhahib al‑'arba`ah, consider it wajib. Also, it is said of Malikis that according to them if the gap between the ashwat were to become inordinate, one should begin sa’y afresh; but if the gap were not prolonged, such as when one discontinues for selling or purchasing something, it is forgivable.
Al‑Sayyid Muhsin al‑Hakim, in his book on the rites of Hajj, says, "It is obligatory, while going and returning, to keep one's face turned towards one's destination .... Therefore, if someone were to turn his face away from it or were to walk backwards, or in a lateral way, it is not correct. However, there is nothing wrong in turning the face this way and that way while continuing to face the destination in the course of movement."
He means that it is obligatory that the body should face Marwah while going and should be toward Safa while returning, and it is not permissible to make the approach with only a shoulder facing the direction of the destination‑‑as may happen due to overcrowding of the pilgrims; also, while moving, the face in particular should remain in the right direction.
Al‑Sayyid al‑Khu'i makes a similar statement in his work on the rites of Hajj; his words are: "It is wajib to face Marwah while going and to be towards Safa while returning. Thus if one turns his back towards Marwah while going and towards Safa while returning, it does not satisfy (lam yujzi', i.e. the conditions for a correct sa’y). Also, one should not turn towards his right or left, neither should he turn back either during the going (dhahab) or during the return (iyab).
One who cannot perform the sa’y, either on foot or on a mount, may depute another to perform it on his/her behalf, and the Hajj would be correct. There is nothing wrong in looking to the right or the left or turning back to look during the coming and the going.
If someone makes more than seven ashwat intentionally, his sa’y is invalid, but not if the lapse was unintentional. If one were to have doubts about the number of the ashwat performed after finishing his sa’y, it is assumed to have been correct and nothing is required of him. The author of al‑Jawahir bases this hukm about the doubt after finishing on the principle of negation of haraj, as well as on tradition.
However, if the doubt were to occur before finishing the sa’y, the author of al‑Jawahir says that there is no difference of opinion about, nor any objection against, the invalidity of the sa`y in case of any doubt about the number of the ashwat performed, whether of having exceeded or fallen short of the required number. In both cases the sa’y at hand is invalid. If one suspects one's having begun from Safa, his sa’y is correct. But if he thinks that he might have started from some other place, it is invalid. Also if one suspects the number of ashwat already performed, and does not know how many one has completed, one's sa`y is invalid.
If one has recorded the number of ashwat performed, but doubts whether one started the first one from Safa or Marwah, he should consider the number of his present shawt and the direction he is facing. If, for instance, the number is an even one (2, 4, or 6) and he is at Safa or facing it, his sa’y is correct; because this shows that he had begun at Safa. Similarly, if the number is odd (3, 5, or 7) and he is at Marwah or facing it. But if the case is reverse, that is in an even shawt he is facing Marwah or in an odd one facing towards Safa, his sa’y is invalid and should be begun anew. (al‑Jawahir)
According to the other schools, the rule is to take the minimum one is certain of having performed, as in the case of salat. (Kifayat al‑'akhyar)
According to Abu Hanifah the Hajj is not invalid even if the sa`y is omitted altogether, because it is not a rukn and can be made good by a sacrifice. (al‑Shi'rani's al‑Mizan)