What is the legal ruling, with evidence, concerning worshippers who do not combine prayers with the Imam due to an excuse such as rain, and leave the mosque because they are not convinced of the permissibility of combining prayers?

If the Imam combines prayers in circumstances where combination is permissible, then it is legislated for the congregant to combine with him, even if the congregant does not experience hardship. If, in this situation, the congregant does not combine with him, then he has gone against the Sunnah and abandoned what is better. However, if he refrains from combining prayers with the Imam because there is no legitimate reason for the Imam to combine them, then there is no blame upon him, for he has done what is incumbent upon him, namely, to refrain from combining prayers in a situation where combination is not permissible.