Soak beans in water overnight. The next day, wash and boil them over low heat until tender (about 1 hour). Drain beans and rinse saucepan. Heat oil and sauté the onion and carrots for 3 minutes. Add tomatoes, salt, pepper, chilli pepper and celery.
As soon as the sauce boils, add the beans and a litre of warm water. Continue cooking until the bean soup is nice and thick. At the end, remove chilli pepper and serve hot.