Is it obligatory to fulfill a vow or offer expiation, after making a vow about a permissible matter while being ignorant of the prohibition of vowing?

"A vow is not forbidden (haram), but rather disliked (makruh). It becomes binding with a formula that expresses commitment, such as 'For the sake of Allah, I vow to do such-and-such.' The statement 'I will give a certain amount to the poor' is not an explicit vow unless the person intends it as a vow. If it is a vow, then it is obligatory to fulfill it when the condition upon which it is suspended is met, and it cannot be canceled."