Ibn Al-Jawzi said-Allah have mercy on him-:
“Beneficial Knowledge is understanding the Islamic fundamentals, Awareness of the only one who deserves to be worshiped (Allah) and extolling Him, and awareness of His rights. Looking into the Biography of the Messenger-Praise and security of Allah be upon him- and his companions, striving to assume their manners and behavior and comprehending what has been narrated from them. That is Beneficial Knowledge.”
[Saydul Khatir pg: 326]