Which clause protects a lender if he does not want the loan to be assumed by another party?

The answer is "Due on sale (alienation) ".

Due on sale (alienation) clause protects a lender if he does not want the loan to be assumed by another party.

A due-on-sale clause is same as alienation, it is a clause in a loan which refers to stipulates that the full adjust of the advance might be called due (reimbursed in full) upon deal or exchange of responsibility for property used to anchor the note. The loan specialist has the right, however not the commitment, to call the note due in such a situation.