What is the ruling on someone who performed Tawaf for 'Umrah and forgot to perform Sa'i, then shaved and exited the state of Ihram, then remembered his omission of Sa'i?

Whoever forgets the Sa'i during 'Umrah must perform it because it is a pillar (rukn). Then, he should shave or shorten his hair to exit the state of ihram. His first shaving is not considered valid because it occurred out of its proper place. However, there is no sin upon the forgetful or ignorant person for the first exiting from ihram and shaving before the Sa'i. Ibn 'Uthaymeen clarified that the 'Umrah is not valid if the Sa'i is omitted. The one who needs to perform Sa'i must re-enter the state of ihram to perform the Sa'i, and then shave or shorten his hair. There is no sin upon him due to his ignorance.