What is the ruling on someone who took off his 'ihram after 'Umrah and then remembered that he had not shaved or cut his hair until after taking off the 'ihram, so he proceeded to cut his hair after taking off the 'ihram and in his home?

There is no fidyah (expiatory offering) upon one who takes off the ihram garments out of forgetfulness or ignorance, so long as he does not persist in doing so after remembering. If he persists, then he must offer the fidyah, which is the well-known position in the madhhab of Imam Ahmad. So, if the forgetful person remembers, he must remove the perfume and take off the (regular) clothes. If he delays in doing so, the fidyah becomes obligatory upon him.