Musnad Ahmad 132:15

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 he said: "Whoever sits in his place of prayer when he finishes the morning prayer until he performs the Duha prayer, saying nothing but good, his sins will be forgiven, even if they were more than the foam of the sea."