Validity of registration of sale deed without possession of immovable property

I am a Registered Owner / Bhumidar of a Property since 10+ Years.....Recently a Person Named "B" had filed a case against me for possession based on Registered sale Deed he had .....That case is under Trial ....meantime "B" SOLD THE PROPERTY TO "C" AND EXECUTED REGISTERED Sale Deed without having physical possession of the property.....how such Sale Deed is valid in law and can sale deed be executed without possession ......kindly guide expert