1036. Commentary: When a Companion (sahabi) attributes an action to the Sunnah with certainty, it holds the same status as the statement or action of the Messenger of Allah (sallallahu alayhi wa sallam), and this is termed as "marfu' hukmi" (elevated by ruling). In the terminology of the hadith scholars (muhaddithin), "Sunnah" refers to the Sunnah of the Messenger of Allah (sallallahu alayhi wa sallam).
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 1036