It is narrated from Sayyiduna Bishr bin Suhaym (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) ordered him to make this announcement during the days of Tashriq: "None will enter Paradise except a believer, and these are days of eating and drinking."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1202