Must I donate a sum of money – after converting it to Saudi Riyals – in exchange for a paper currency I took from a foreign worker in my childhood, given the feeling that she did not give it wholeheartedly?

A Muslim's property is sacrosanct, and it is not permissible to take it except with his willing consent. Therefore, whoever takes money from another out of shyness, without the latter's consent, that money is not permissible for him, and he must return it to its owner. If he is unable to deliver it to him, he should give it as charity on his behalf. This ruling does not differ whether the money was taken before or after puberty, for a minor is held responsible for financial rights he infringed upon before reaching maturity.