Musnad Ahmad 132:6

Hassan narrated to us, Ibn Lahi'ah narrated to us, Zabban narrated to us, from Sahl ibn Mu'adh, from his father, from the Messenger of Allah, may Allah bless him and grant him peace, that a man asked him and said: "Which Jihad is greatest in reward?" He said: "The one among them who remembers Allah, Blessed and Exalted is He, the most." He said: "Then which of the fasting people is greatest in reward?" He said: "The one among them who remembers Allah, Blessed and Exalted is He, the most." Then he mentioned to us the prayer, the Zakat, the Hajj, and the charity, and for all of that, the Messenger of Allah, may Allah bless him and grant him peace, was saying: "The one among them who remembers Allah, Blessed and Exalted is He, the most." Abu Bakr said to Umar: "O Abu Hafs, those who remember [Allah] have taken away all the good." The Messenger of Allah, may Allah bless him and grant him peace, said: "Yes."