With a Disney base ticket, you’re welcome to leave and re-enter the same theme park as many times as you like during the same day. So, if you want to visit the Magic Kingdom in the morning, go back to your hotel room for a nap, and return to the Magic Kingdom in the evening, then you do not need a Park Hopper ticket.
Also know, how many times can you enter a Disney park?
To enter a park, both a park reservation AND valid admission for the same park on the same date are required for each person in your party ages 3 and up (limit one park per day). Guests who purchased a ticket or annual pass with Park Hopper benefits are now able to visit more than one park per day after 2 PM.