Is this seclusion valid, and is it permissible to adopt the Hanbali position regarding the establishment of the dowry (mahr) and the right of return (raj'ah) through it?

The valid seclusion (al-khalwa al-sahiha) that carries the ruling of consummation (ad-dukhool) is one in which sexual intercourse can ordinarily occur. Seclusion in a closed room, where no one can enter without permission, is a valid seclusion by which the mahr (dowry) becomes binding according to the majority of scholars, and by which the right of return (raj'ah) is established according to the Hanbalis. There is no blame upon someone who adopts the view of the Hanbalis in this matter, as long as they are confident in the validity of the opinion and are not merely following their desires.