In general, you will have to pay him the salary for the notice period. The employee has resigned and is willing to serve the notice period as required by the law. You are asking him not to come to the office for that period, for your convenience. Therefore, you will have to pay him for that period.
In practice, you can always offer to relieve him with immediate effect. If he accepts the offer, then he will not get paid for the remaining period. (But you need to make that clear when you offer immediate relieving). If he has the option of joining the new company earlier, he may opt for it. Or in many cases, he will choose it to get time to relax before joining a new company, where work will be hectic and stressful initially.
Concept of "Gardening Leave"
Globally, most companies have a concept of "Gardening Leave." This is a period of notice where the employee is asked not to come to the office but not to join the new company. He is to be available on call until the end of the notice period. This has the advantage of being able to call him back to the office for any clarification or for an explanation of training that his replacement will need.
Ultimately, no one is going to court for one month's salary. The cost and hassles are too high. However, it will leave a bitter taste, and if you need anything in the future, you will not get it from him. (Say a month later some matter has come up, which you need to ask him what he had done about it). Remember that many things are not recorded in files.