It is permissible to perform 'Umrah during the months of Hajj
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، ح وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، - وَاللَّفْظُ لَهُ - حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنِ الْحَكَمِ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ، - رضى الله عنهما - قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " هَذِهِ عُمْرَةٌ اسْتَمْتَعْنَا بِهَا فَمَنْ لَمْ يَكُنْ عِنْدَهُ الْهَدْىُ فَلْيَحِلَّ الْحِلَّ كُلَّهُ فَإِنَّ الْعُمْرَةَ قَدْ دَخَلَتْ فِي الْحَجِّ إِلَى يَوْمِ الْقِيَامَةِ " .
Ibn 'Abbas (Allah be pleased with them) reported Allah's Messenger (ﷺ) as saying: This is the 'Umra of which we have taken advantage. So he who has not the sacrificial animal with him should get out of the state of Ihram completely, for 'Umra has been incorporated in Hajj until the Day of Resurrection,