Reg: is a notarised release deed is valid ???

am from a hindu family ,the property is our ancestor property, which is bought on 1937 and partitioned to my father via a registered partition deed on 1996 , my self and my sister are the legal heirs of my father (he is still alive) , my sister executed a release deed to my father on 2004 , which is only notarised, but not registered , my query is that the notarised release deed is legally valid? or only a registered release deed is mandatory for my father to pledge this property for a bank loan.