Farwah bin Nawfal al-Ashja'i says that Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "Indeed, Mu'adh was an ummah, devoutly obedient to Allah, upright." I said to myself: Abu Abd al-Rahman has made a mistake; the verse is rather "Indeed, Ibrahim." (Sayyiduna Abdullah (may Allah be pleased with him)) said: "Do you know what the ummah is, and what the qanit is?" I said: "Allah knows best." He said: "The ummah is the one who teaches people good, and the qanit is the one who is obedient to Allah and His Messenger; and Mu'adh bin Jabal (may Allah be pleased with him) was just like that: he taught good and was obedient to Allah and His Messenger."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9911