Mishkat al-Masabih
He reported God’s messenger as saying, “An 'umra is an expiation for sins committed between it and the next, but a hajj which is accepted will receive no less a reward than paradise.” Bukhari and Muslim.
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «الْعُمْرَةُ إِلَى الْعُمْرَةِ كَفَّارَةٌ لِمَا بَيْنَهُمَا وَالْحَجُّ الْمَبْرُورُ لَيْسَ لَهُ جَزاءٌ إِلا الجنَّةُ»
Reference