Is a Muslim sinful if he acts upon the opinion of Ibn Taymiyyah and Ibn al-Qayyim regarding the non-occurrence of a menstruating woman's divorce, thereby contradicting the view of the Four Schools of Thought that you prioritize?

It is permissible to follow the opinions of trustworthy scholars, such as Sheikh Al-Islam Ibn Taymiyyah and those who agreed with him, as long as it is not for the purpose of seeking out dispensations, but rather out of trust in them and following their lead. This is because it is not obligatory to follow only the four madhhabs; rather, it is permissible to follow other reliable scholars whose opinions on a particular issue have been preserved.