Hadith 4:858
Hussain bin Ali narrated to us, from Abu Musa, from al-Hasan, who said: When the six days—which some people fast after Ramadan as a voluntary act—were mentioned in his presence, he used to say: "Allah has been pleased with this month for the entire year."
حدثنا حسين بن علي عن أبي موسى عن الحسن قال إذا ذكر عنده ستة أيام التي يصومها بعض الناس بعد رمضان تطوعا كان يقول لقد رضي الله بهذا الشهر للسنة كلها