´It was narrated that Abu Hurairah said:` "The Messenger of Allah said: 'Whoever fasts Ramadan out of faith and in the hope of reward, he will be forgiven his previous sins." '
Hadith ReferenceSunan an-Nasa'i / The Book of Fasting / Hadith: 2207
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح بخاري
Hadith Takhrij«صحیح البخاری/الإیمان 28 (38)، سنن ابن ماجہ/الصوم 2 (1641)، (تحفة الأشراف: 15353) ، مسند احمد 2/232 (صحیح)»