Abu Huraira reported God’s messenger as saying, "When Ramadan begins the gates of heaven are opened." A version has, "The gates of paradise are opened, the gates of jahannam are locked, and the devils are chained." Another has, "The gates of mercy are opened." (Bukhari and Muslim).
Hadith Referenceمشكوة المصابيح / كتاب الصوم / 1956
Hadith Gradingالألبانی:مُتَّفَقٌ عَلَيْهِ | زبیر علی زئی:متفق عليه
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «متفق عليه، رواه البخاري (1899) و مسلم (1079/2)»