Sahih Al Bukhari – Book of Minor Pilgrammage (Umra)

Volumn 003, Book 027, Hadith Number 001. 
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Narated By Abu Huraira

Razi Allah Anhu

 : Allah's Apostle

 said, "(The performance of) 'Umra is an expiation for the sins committed (between it and the previous one). And the reward of Hajj Mabrur (the one accepted by Allah SWT) is nothing except Paradise."