Ruling On The Exiting Of Less Than Excused Amount Of Najasah In Wudu
This is fiqh, which is a human endeavour and is prone to be subjective at scholarly level. What is concrete is Sunnah in this regard which clearly establishes the nullifiers of Wudu. The next thing is fiqh which deals with different application matters like the ones mentioned by you. We know that urination and defecation nullify the Wudu. And it is only logical that urination and defecation need to be identifiable so that the person should be aware that his wudu has been nullified. In case of traces which cannot be identified, the person is not liable to redo his wudu because that would be equivalent to putting undue burden on the Person which is against the Quranic principles of ‘ Yusar ‘ and ‘ La-yukallifullahu Nafsan illa wusaha ‘. When a person knows it is sweat then it is sweat, traces of impurity which are not identifiable should be ignored. Btw, if one opts for the option as mentioned above with reference to Ibn-e-Qudamah, then it would also made it obligatory for the person to first wash himself properly the way he would do so after urination or defecation because now his situation has been made similar to that of a person who has defecated or urinated.