All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If you had purchased the land with the intention of owning it and not with the intention of trading with it, then you are not obliged to pay Zakah on it whether you sold it with your own choice or were forced to do so by the relatives of its previous owner. Rather, you are obliged to pay Zakah on its price –after selling it – if it reaches the Nisaab (the minimum amount liable for Zakah) and a whole lunar year elapses on it while in your possession.
For more benefit, please refer to Fataawa 83761 and 86227.
Allaah Knows best.