Musnad Ahmad 8:174

Ya'la ibn 'Ubayd narrated to us, Musa narrated to us, from Mus'ab ibn Sa'd, from his father, who said: We were sitting with the Messenger of Allah, may Allah bless him and grant him peace, and he said: "Is one of you unable to earn one thousand good deeds every day?" A questioner from among those sitting with him asked him: How can one of us earn one thousand good deeds every day, O Messenger of Allah? He said: "He performs one hundred tasbihs (saying 'SubhanAllah'), and one thousand good deeds are written for him, or one thousand sins are removed from him."