It is narrated from Sayyiduna Bishr bin Suhaym (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) ordered him to make this announcement during the days of Tashriq: "None will enter Paradise except a believer; these are days of eating and drinking."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1203