Promotion of this idea, that the six day of Shawwal are somehow aberrant and to not be fasted - is incorrect for several reasons:
1- The fundamental evidence for the legality of an act is found in the primary texts of Islam, namely the Hadith in Sahih Muslim encouraging this act. https://twitter.com/OfficialASI/status/1136331330080399361

2- The generality of the text needs no support from the actions of the Companions.
3- The Companions were people who acted according to the general texts, this is evidenced by Abu Ayyub teaching the public this Hadith, in Shawwal, after having fasted Ramadan.

4- To make the permissibility or preference of an act substantiated by primary texts (Quran & Sunna) contingent on the actions of the Companions is to make the infallible contingent on the fallible.

5- The broad narration of this act in the Hadith, and it's encouragement in almost all Fiqh texts, shows that Imam Malik was less informed than others on this issue and that it's practice was known to early Muslims.