Purity in sa'y is like purity in tawaf. There is no reliability upon it.

627 - Issue: He said: (And if the prayer is commenced, or a funeral procession is present while he is performing tawaf or sa'y, [he leaves and prays], then when he prays, he builds [continues from where he left off]).

The entirety of this matter is that if he has engaged in tawaf or sa'y, then the obligatory prayer is commenced, he should pray with the congregation, according to the view of the majority of scholars, among them Ibn Umar, Salim, 'Ata', al-Shafi'i, Abu Thawr, and the People of Opinion (Ashab al-Ra'y). This has been narrated from them regarding sa'y as well. Malik said: He should proceed with his tawaf and not interrupt it, [unless he fears that he will harm the prayer time; for tawaf is a prayer, so he should not interrupt it] for another prayer. Our evidence is the statement of the Prophet (may the peace and blessings of Allah be upon him): "When the prayer is commenced, there is no prayer except the obligatory one." Tawaf is a prayer, so it falls under the generality of this report. If this is established regarding tawaf around the House, with its emphasis, then it is even more applicable to sa'y between al-Safa and al-Marwa, especially since it is the view of Ibn Umar and those we have named among the scholars, and we do not know of any opposing them in their era. And when he prays, he builds upon his tawaf and his sa'y, according to the view of those we have named among the scholars. Ibn al-Mundhir said: We know of no one who differed regarding this, except al-Hasan, for he said: He must restart. The view of the majority is better; because this is an act prescribed during the course of tawaf, so it does not interrupt it, like a minor [interruption]. The same ruling applies to the funeral prayer if it is present; he prays over it and then continues his tawaf, because it will be missed if he occupies himself otherwise. Ahmad said: It begins