What are the limits of the mustache that a Muslim should trim to adhere to the Sunnah?

The mustache is the hair that extends over the mouth, and it includes the "sabalan" (the two ends of the mustache). The correct approach is to trim the sabalan due to the prophetic traditions that command trimming them and acting contrary to the People of the Book and the Majus (Zoroastrians) who let them grow long. Indeed, Ibn Umar used to trim his sabalan. There are also other scholarly opinions, such as the permissibility of leaving the sabalan untrimmed.