Insist (= declare firmly)
Incorrect : He insisted to his innocence.
Correct: He insisted on his innocence.
Incorrect : She insisted for going there.
Correct : She insisted on going there.
Note: But the word ‘persist’ is different from ‘insist’ and it also takes a different preposition.
For example:
Incorrect : He persisted on his foolish ideas.
Correct : He persisted in his foolish ideas.