Sunan an-Nasa'i, Volume 3, Book 24, Hadith 2817 (DarusSalam) ⓘ

It was narrated from Ibn Abbas that the Prophet said: This is 'Umrah that we have benefited from. Whoever does not have a Hadi with him, let him exit Ihram completely. Now 'Umrah is permissible during the months of Hajj."

أَخْبَرَنَا مُحَمَّدُ بْنُ بَشَّارٍ، قَالَ حَدَّثَنَا مُحَمَّدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنِ الْحَكَمِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ هَذِهِ عُمْرَةٌ اسْتَمْتَعْنَاهَا فَمَنْ لَمْ يَكُنْ عِنْدَهُ هَدْىٌ فَلْيَحِلَّ الْحِلَّ كُلَّهُ فَقَدْ دَخَلَتِ الْعُمْرَةُ فِي الْحَجِّ ‏" ‏ ‏.‏