What is the ruling on praying in ritually impure clothes if the worshiper has no other clothes?

Prayer is not valid in a ritually impure garment if the worshipper is able to pray in a ritually pure garment. This can be achieved in three ways: either by washing the impure spot, or by removing the impure clothes if his 'awrah (private parts) are covered, or by praying in the impure garment, in which case he is excused and his prayer is valid, if he cannot find a pure garment or is unable to remove the impurity.