Uncooked rice can contain bacillus cereus, which remains on it during cooking. It's best not to leave cooked rice to sit out at room temperature for longer than it needs to because any bacteria or toxins multiply at room temperature.  Serve rice as soon as it's cooked and let it cool for a maximum of an hour then refrigerate it in rice containers, plastic containers, or mason jars. If you aren't sure how long it's been out, it's best to throw it out rather than risk eating it, especially since rice is a very cheap option anyway. When you reheat the rice, ensure it's very hot throughout, and don't reheat rice more than once. Following these tips should minimize your chances of any ill effects from spoiled rice.