The Messenger of Allah ﷺ entered the state of ihram for Hajj. He arrived on the fourth day of Dhul-Hijjah, then led us in the dawn prayer at al-Batha. After that he said, "Whoever wishes to make it an Amra may do so."
حدثنا روح حدثنا شعبة عن أيوب عن أبي العالية البراء
أهل رسول الله ﷺ بالحج فقدم لأربع مضين من ذي الحجة فصلى بنا الصبح بالبطحاء ثم قال من شاء أن يجعلها عمرة فليجعلها
Its isnad is sahih. Abu Aliyah Bara's name was Ziyad bin Fayruz, and this is stated definitively by Bukhari in al-Kabir 2/1/334 and by Sam'ani in al-Ansab, though other views have been given. The correct view is what we have stated, and he is a trustworthy Follower (tabi'i thiqah). Bara is with a doubled ra, derived from the paring/fashioning of things. See also 2360, 2641, 3128, 3172, 3395.