Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "When Ramadan begins, the gates of Jannah are opened, the gates of Hell are closed, and the devils are chained."[Al-Bukhari and Muslim]. (FR)
App reference (FR): Book 9, Hadith 230 (FR)
Arabic/English book reference (FR): Book 9, Hadith 1220 (FR)