In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Sufyaan Ibn Uyaynah [rahimahullaah] used to say: Indeed, the Messenger [sallal-laahu-alayhi-wasallam] is the greatest criterion [i.e. amongst mankind and Jinn] and all affairs are presented to him [i.e. for judgement and judged] based on his manners, path and guidance; so whatever is in agreement with this is truth, and whatever is in opposition is falsehood.

[Al-Jaami Li-Akhlaaq Ar-Raawi Wa Aadaab As-Saami’  page 8]