How to deal with and act in doubtful matters?

Tuhaf al uqul

وقال عليه السلام: أورع الناس من وقف عند الشبهة، أعبد الناس من أقام على الفرائض، أزهد الناس من ترك الحرام، أشد الناس اجتهادا من ترك الذنوب

 

And said (Imam Hasan al Askari)(as): "The pious among the people is one who would stop at doubt, the worshiper among the people is one who would stand upon the obligations, the abstinent among the people is one who would abandon the haram (unlawful), the most struggling/hardworking among the people is one who would abandon sins."