Reference: Duroos wa Fataawa al-Hajj – Volume 1, Page 18, No.28
Question: Whilst performing the sa’ee, the Maghrib prayer took place, so I prayed and thereafter [continued with and] completed the sa’ee; so is that sa’ee correct?
Response: Yes [it is]; if, whilst performing the tawaaf or the sa’ee the [obligatory] prayer takes place, the pilgrim should [join the congregation and] pray. Then, after concluding [the prayer], he continues [the tawaaf or the sa’ee] from the circuit [or lap] where he left off and completes [it].