This questioner says:

السلام عليكم ورحمة الله وبركاته

If a student of knowledge utters innovation and calls to it, and he is one with Fiqh and (knowledge of) Hadeeth; does his speech of innovation necessitate an invalidation of his knowledge and his (knowledge) of hadeeth, and not to (benefit from) him unrestrictedly?

Shaykh Sālih bin Fawzān Al-Fawzān:

Yes, he is not to be trusted; the one who is an Innovator is neither to be trusted nor his knowledge, nor (to have) a lackadaisical (stance) towards him. That is because if you (have) a lackadaisical (stance) towards him, the student will be influenced by his Shaikh-he will be influenced by his teacher. Therefore, it is obligatory to be distanced from the people of innovation, and the Salaf (pious predecessors) used to forbid (others) from sitting with the innovators, visiting and going to them; so that their evil is not spread to the one who sits with them and mixes with them. نعم