Ibn ‘Abdil Barr رحمه الله explained in his colossal book at Tamhīd the importance of adhering and respecting the sunnah. He mentions, “There is not anyone from Allah’s creation except that his speech is either accepted or rejected, except for the Prophet صلى الله عليه وسلم as his speech is not left except that which he himself left by either abrogating it by another statement of his or an action from him.

Legislative proof is in what he صلى الله عليه سلم said and proof is not in what someone else says. Similarly, it is not [permissible] for anyone from the scholars to affirm a hadith of the Prophet صلى الله عليه وسلم and then reject it without claiming that it has been abrogated or for some other valid legislated reason. And if anyone from the scholars did this, his uprightness would be rendered null and void in addition to not be taken as an Imām [1].
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[1] Fatāwā ‘Ulamā al Mālikiyah fī Taqrīr ‘Aqīdah Ahl Sunnah, pg. 156.
at Tamhīd, v.1, pg.159, 366, v.2, pg.27, v.10, pg.115, v.19, pg.274.