Is custom to be acted upon instead of building upon the original principle in cases of doubt, as in the example of someone whose custom is to pray on time and doubts whether he has prayed or not, and what is the meaning of "custom"?

The word "habit" in the Arabic language refers to: a recurring custom. In technical terms, it is: what people consistently do based on reason, returning to it repeatedly.

Whoever is accustomed to praying on time and then doubts whether they have prayed or not, must pray again; this is giving precedence to the original state, which is that the prayer remains an obligation until its performance is confirmed. According to Abu Hanifa, if the doubt occurs after the time for the prayer has elapsed, then praying again is not obligatory.