Musnad Ahmad 416:1

Abdullah ibn Ahmad said: Abu Malik al-Hanafi Kathir ibn Yahya ibn Kathir al-Basri narrated to me, he said: Thabit Abu Zayd narrated to us, he said: Hilal ibn Khabbab narrated to us, from Ikrimah ibn Khalid al-Makhzumi, he said: A chief from the chiefs of Quraysh narrated to me, from his father, that he heard it from the mouth of the Messenger of Allah, peace and blessings of Allah be upon him, who said: "Whoever fasts Ramadan, Shawwal, Wednesday, and Thursday shall enter Paradise."