In a 6 quart Dutch oven or heavy pot, melt the butter over medium-high heat and cook the sausage until lightly browned. Add the onions and cook until soft and translucent, 5-6 minutes. Add the celery and garlic and cook until softened, 4-5 minutes. Add the chicken, chicken broth, hot sauce (if using), bay leaves, thyme, salt and pepper and bring it to a boil. Reduce to heat to low, cover, and simmer for 45-60 minutes or until the chicken is done. Discard the bay leaves and thyme sprigs. Remove the chicken, let it sit until cool enough to handle, then remove the meat and coarsely chop it. Return the chicken to the pot and add the rice. Bring it to a boil, then reduce the heat to low, cover, and simmer for 20-25 minutes, stirring once or twice, until the rice is tender and has absorbed most of the broth. If it's too dry, add more broth or water as needed. Add salt and pepper to taste. Turn off the heat and let it sit covered for 10 minutes. Serve garnished with some chopped parsley and green onions.