We know Harmuzan was brought back to Madinah as a slave. He was satrap of Khuzestan. There was another salve named Firoz, he belonged to a man named Mughira.
Firoz came to Umar to complain about his master. Umar listened and afterwards asked Firoz (who was blacksmith and carpenter) to build him a windmill.
Firoz replied, but before that he tacitly said, “if allowed to live.”
Umar heard this but chose to ignore it. Next morning when he was leading prayers and went in Sajda was stabbed by Firoz six times with poisoned dagger.
Firoz stabbed himself too. Upon his deathbed, he asked Abdur Rehman bin Auf to be his successor, but Rehman declined his offer.
He then formed six men committee and asked them to appoint his successor within 3 days.
He breathed his last on November 3 644.
For complete Islamic history notes click here.