I bought land from a person who had acquired it using money he got from selling marijuana اشتريت أرض من رجل يتاجر بالحشيش

Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.

To proceed:

In response to your question, we say, and with Allah Almighty lies all success:
The land is not prohibited to you even though the previous owner had bought it using unlawful earnings. This is because prohibition is related to him and not you. Moreover you acquired the land legally through a valid contract. With regards to your wife’s claim that she has a share on this land; if there was an agreement between you and her, or you gave it to her as a gift then you should do what you agreed. But if you spent your money to buy this land without any contribution from your wife then it is your land not hers. The seller’s saying: he sold the land is of no effect because consideration is given to the one who paid the price. However, your ex-wife’s claim that the fax is evidence is a legal case between your wife and the owner of the land, the competent authority to settle that is the court. However what was earlier mentioned is applicable in terms of theory and ruling. May Allah grant you goodness and success