Restraint of trade agreement
Q: I would like to know if a restraint of trade agreement is permissible in an Islamic sale.
Example: I am selling my cellphone business to Zaid. In the sale agreement a clause is added that I, the seller, is not allowed to trade in the same field of business for a stipulated period (e.g. 5 years). Will such a clause be permissible? If not will the adding of such a clause nullify the entire sale? Or will the clause be impermissible and the rest of the sale be correct?