Which one of the following is not essential for a valid gift or Hiba under the Mohammedan Law?

A valid hiba requires a declaration of the gift by the donor, acceptance by or on behalf of the donee, and delivery of possession, actual or constructive. "Written documentary proof of the gift" is not essential: in Hafeeza Bibi v Shaikh Farid (2011) the Supreme Court held that an oral gift satisfying these three conditions is valid, and that reducing it to writing does not by itself make registration compulsory.