Abdur-Rahmaan al-Awzaa’ee 157 AH (May Allah have mercy on him) said:

العلم ما جاء به أصحاب محمد صل الله عليه و سلم فما كان غير ذلك فليس بعلم

“Knowledge is what comes from the companions Muhammad peace be upon him, so whatever is other than that is not knowledge”

Taken from: Ibn Rajab’s “Fadl ilm Salaf ala ilm Khalaf” under the chapter “Afdal ‘Uloom”