Jundub Radiyallahu 'anhu narrates that Rasullullah Sallallahu 'alaihi wasallam said: He who interprets the Qur'an according to his opinion and that happens to be correct, even then he has erred. (Abu Dawud: 3652)
Note: This means, that if someone interprets the Qur'an in the light
of his own opinion and that interpretation incidentally turns out to be
correct; even so he has erred, because he did not refer (for this
commentary) to the Prophet's Ahadith and nor to the 'Ulama of this
Ummah. (Mazahir-e-Haque)