Hadith #1478 (Sunan Ibn Majah)
Book: Fasting
Narrator(s): Abu al-Khattab al-Damashqi أبو الخطاب, Anas ibn Malik, Hisham bin 'Ammar bin Nasayr هشام بن عمار بن نصير

“Fast Shawwal.” So he forsook the sacred months and he continued to fast Shawwal until he died.

Source: https://parallelquran.com/hadith/sunan-ibn-majah-1478/