Musnad Abu Ya'la al-Mawsili 6:141

Mu'alla narrated to us, Abu 'Awanah narrated to us, from Musa al-Juhani, from Mus'ab bin Sa'd, from his father, who said: The Messenger of Allah (ﷺ) said: "Is one of you unable to earn one thousand good deeds every day?" A man from those sitting with him said: "How is one thousand good deeds written for him?" He said: "He performs one thousand tasbihs (saying SubhanAllah), so one thousand good deeds are written for him, and one thousand sins are erased from him."