There was a little girl (six years old) who was fasting in Ramadhan, even though it is not obligatory for people below the age of puberty. She was in school, and at lunch time, when all the other children went out to eat and have lunch, she sat in the classroom, because she was fasting.
Her (non-muslim) teacher thought that she was too young to fast, and so said that it was not necessary, and she could eat a little. The girl still didn’t eat.
Then the teacher said: “Your parents are not here, it doesn’t matter if you eat a little”. The girl replied: “I am not fasting for my parents, I am fasting for Allah”.
This simple statement had such a profound effect on the teacher, that later she accepted Islam.