Answer
(Fatwa: 136/136/M=1433)
If the dealing is to the extent of agreement and formal ijab-o-qubool of sale is not done then it is not lawful to sell it to someone else. And if you finalise the dealing by ijab-o-qubool at the time of buying land or house and pay some price of land with promise to pay the remaining price at a later time, then in this case you can sell it to others after having possession of it even before its registration.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband