Musnad Ahmad 33:630

Musa narrated to us, Ibn Lahi'ah narrated to us, from Abu al-Zubayr, from Jabir, that Nu'man ibn Qawqal came to the Messenger of Allah, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, have you considered if I pray the prescribed prayers, fast Ramadan, treat the forbidden as forbidden, and treat the lawful as lawful, and I do not add anything to that, shall I enter Paradise?" He said: "Yes." He then said: "By Allah, I will not add anything to that."