Musnad Ahmad 32:1530

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Al-Zuhri mentioned, from Uways ibn Abi Uways, an ally of the Banu Tamim, from Anas ibn Malik al-Ansari, that the Messenger of Allah, peace and blessings of Allah be upon him, said: "This Ramadan has come. The gates of Paradise are opened in it, the gates of the Fire are closed in it, and the devils are chained in it."