It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Umrah is an expiation for all the sins committed between the present Umrah and the previous Umrah, and the only reward for an accepted Hajj is Paradise."
Hadith Referenceصحيح ابن خزيمه / جماع أبواب ذكر العمرة وشرائعها وسننها وفضائلها / 3072