Sayyiduna Anas bin Malik (may Allah be pleased with him) states: I heard the Prophet (peace and blessings be upon him) say: "This is Ramadan, which has come. In it the gates of Paradise are opened, in it the gates of Hell are closed, and in it the devils are locked up. So may that person be far removed who finds the month of Ramadan and is then not forgiven. If he is not forgiven in this month, then when will he be?"
Al-Tabarani recorded it in al-Mu'jam al-Awsat. Its chain contains a narrator, al-Fadl bin Isa al-Raqashi, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصيام / 4788