Is it obligatory for the pilgrim performing Tamattu' Hajj, after completing his 'Umrah on the seventh day of Dhul-Hijjah, to remove his ihram garments and exit the state of ihram, then re-enter ihram for Hajj on the eighth day, or is it permissible for him to remain in his ihram garments between 'Umrah and Hajj?

It is not obligatory to remove the clothes of Ihram after performing Umrat al-Tamattu'. It is permissible to keep them on and enter into Ihram with them for Hajj on the eighth day. The essential aspects are the actions of Umrah, which include circumambulation (Tawaf), rushing (Sa'i), and shortening the hair (Taqsir). However, it is preferable to remove the clothes of Ihram and wear regular clothes to signify the completion of ritual disengagement (Tahallul).