Musnad Ahmad 132:5

Hassan narrated to us, Ibn Lahi'ah narrated to us, he said: And Yahya ibn Ghaylan narrated to us, he said: Rashdin 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, who said: "Indeed, the remembrance (dhikr) in the path of Allah the Exalted is multiplied above spending by seven hundred times." Yahya said in his narration: "By seven hundred thousand times."