Musnad Ahmad 830:106

Yazid ibn Harun narrated to us, Hammad ibn Salamah informed us, and Rawh narrated to us, Hammad ibn Salamah narrated to us, from Salim Abu Hatim—and Rawh said: from Salim Abu Ubayd Allah ibn Salim—and Affan narrated to us, in a hadith he mentioned from Hammad, from Salim Abu Ubayd Allah, and he is also known by the kunya Abu Hatim, from Abd al-Rahman ibn Abi Bakrah, from his father, from the Prophet, peace and blessings of Allah be upon him, who said: "Two months of Eid do not decrease: Ramadan and Dhu al-Hijjah."