needn't

I needn’t have washed the car: shortly after it started raining.

‘Oh no,’ said the boy casually. ‘I won’t think much about them, mother. You needn’t worry. I wouldn’t worry, mother, if I were you.’ / ‘If you were me and I were you’, said his mother, ‘I wonder what we should do!’ / ‘But you know you needn’t worry, mother, don’t you?’ the boy repeated.