Ibn 'Abbas (Allah be pleased with them) reported:

Allah's Messenger (ﷺ) came along with his Companions when four days had passed out of ten days (of Dhu'l-Hijja) and they were pronouncing Talbiya for Hajj, and he (the Prophet) commanded them to change (this Ihram) into that of 'Umra.

وَحَدَّثَنَا هَارُونُ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا مُحَمَّدُ بْنُ الْفَضْلِ السَّدُوسِيُّ، حَدَّثَنَا وُهَيْبٌ، أَخْبَرَنَا أَيُّوبُ، عَنْ أَبِي الْعَالِيَةِ الْبَرَّاءِ، عَنِ ابْنِ عَبَّاسٍ، - رضى الله عنهما - قَالَ قَدِمَ النَّبِيُّ صلى الله عليه وسلم وَأَصْحَابُهُ لأَرْبَعٍ خَلَوْنَ مِنَ الْعَشْرِ وَهُمْ يُلَبُّونَ بِالْحَجِّ فَأَمَرَهُمْ أَنْ يَجْعَلُوهَا عُمْرَةً ‏.‏