The ruling on one who performed Hajj and 'Umrah but only did the sa'y (walking between al-Safa and al-Marwah) once

Question:
May Allah reward you with good. If a person has completed both Hajj and 'Umrah, but only performed the sa'y once for both rites, is his work valid? And if his work is not valid, what is obligatory for him?

Answer:
There is a distinction here. If he combined (qiran) Hajj and 'Umrah with a single state of ihram, then one sa'y is sufficient for both, one tawaf (circumambulation) is sufficient for both, and one sa'y is sufficient for both; because the 'Umrah is included in the Hajj, becoming part of the acts of Hajj. However, if he performed tamattu' (combining 'Umrah and Hajj with a break between them), then it is obligatory for him to perform two sa'ys: one for Hajj and one for 'Umrah. He performs the 'Umrah first with its tawaf, its sa'y, and its shortening of the hair, and exits the state of ihram from it. Then he enters the state of ihram for Hajj and performs the tawaf of ifadah on the day of 'Id or after it, and performs the sa'y between al-Safa and al-Marwah for Hajj. If he neglected this in this situation, then his Hajj remains incomplete, and it is obligatory for him to perform the sa'y, even after a long period, even after years. He returns to Makkah and performs the sa'y for Hajj.
And he performs the tawaf of farewell after it, because his first farewell was not valid, as it occurred before completing the rites of Hajj. So he performs the sa'y for the past Hajj, and performs the tawaf of farewell. And if he engaged in sexual intercourse during this period, then he must slaughter a sheep in Makkah and distribute it to the poor of the Haram, and his Hajj is valid, if Allah wills.