What is the ruling on someone who finishes the 'ifrad' (Hajj al-Ifrad) and then performs 'Umrah?

Performing Umrah after Hajj has no basis in the Sunnah, and the Companions did not do it. The only exception is what happened with Aisha (may Allah be pleased with her), as her Umrah transformed into Qiran due to menstruation, so the Prophet (peace be upon him) permitted her to perform a compensatory Umrah after Hajj. Thus, if a woman is in the same circumstances as Aisha, there is no harm for her in performing Umrah. However, what some pilgrims do, performing Umrah after Hajj without a শরعي (Shar'i - Islamic legal) reason, has no basis in the Sunnah. But if the pilgrim has performed Hajj Al-Ifrad (Hajj performed alone without Umrah) and it is difficult for him to return later to perform Umrah (which is obligatory), then he may perform it after Hajj by going to the Hil (area outside the Haram boundary) and entering into Ihram from there.