I just remembered something. According to Syed Sistani :
213. If before an unbeliever becomes a Muslim, his wet dress touched his body, as an obligatory precaution, it should be avoided, regardless of whether it is on his body or not.
Since it is only an obligatory precaution to avoid something a muslim touched with his wet body before his conversion/reversion, I wonder if there is a marja who says that you don't need to avoid it. Does anyone know a marja who says that ?
Are you sure only nasibi are najis ? Because Ay. Sistani says any kafir is najis :
107. An infidel i.e. a person who does not believe in Allah and His Oneness, is najis. Similarly, Ghulat who believe in any of the holy twelve Imams as God, or that they are incarnations of God, and Khawarij and Nawasib who express enmity towards th e holy Imams, are also najis. And similar is the case of those who deny Prophethood, or any of the necessary laws of Islam, like, namaz and fasting, which are believed by the Muslims as a part of Islam, and which they also know as such. As regards the people of the Book (i.e. the Jews and the Christians) who do not accept the Prophethood of Prophet Muhammad bin Abdullah (Peace be upon him and his progeny), they are commonly considered najis, but it is not improbable that they are Pak. Ho wever, it is better to avoid them.
Unfortunaly, I remember having red an hadith from an Imam as who said that the one who has doubts about Allah swt is a kafir. Here is it (https://www.al-islam.org/qalbe-saleem-immaculate-conscience-ayatullah-sayyid-abdul-husayn-dastghaib-shirazi/fourth-disease)