Sahih Muslim , Book 7, Hadith 2859 (USC-MSA) ⓘ
Ibn 'Abbas (Allah be pleased with them) 'is reported to have said: The Messenger of Allah put on Ihigm for Hajj. When four days of Dhu'l-Hijja were over, he led the dawn prayer, and when the prayer was complete, he said: He who wants to change it to Umra may do so.
حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ أَيُّوبَ، عَنْ أَبِي الْعَالِيَةِ، الْبَرَّاءِ أَنَّهُ سَمِعَ ابْنَ عَبَّاسٍ، - رضى الله عنهما - يَقُولُ أَهَلَّ رَسُولُ اللَّهِ صلى الله عليه وسلم بِالْحَجِّ فَقَدِمَ لأَرْبَعٍ مَضَيْنَ مِنْ ذِي الْحِجَّةِ فَصَلَّى الصُّبْحَ وَقَالَ لَمَّا صَلَّى الصُّبْحَ " مَنْ شَاءَ أَنْ يَجْعَلَهَا عُمْرَةً فَلْيَجْعَلْهَا عُمْرَةً " .
also referenced under: Book 15, Hadith 218 (In-Book) & Hadith 1240 (Reference)