"The Messenger of Allah came on the fourth day of Dhul-Hijjah having entered Ihram for Hajj. He prayed Subh in Al-Batha and said: 'Whoever wants to make it Umrah, let him do so.'" (Using translation from Nasāʾī 2871)
أَنَّهُ قَالَ أَهَلَّ رَسُولُ اللهِ ﷺ بِالْحَجِّ فَقَدِمَ لِأَرْبَعٍ مَضَيْنَ مِنْ ذِي الْحِجَّةِ فَصَلَّى بِنَا الصُّبْحَ بِالْبَطْحَاءِ ثُمَّ قَالَ مَنْ شَاءَ أَنْ يَجْعَلَهَا عُمْرَةً فَلْيَجْعَلْهَا