I mentioned to Ibn Umar that Anas had told us that the Prophet ﷺ entered the state of ihram for both an Umra and a Hajj.Ibn Umar said, "Anas is mistaken. The Messenger of Allah ﷺ entered ihram for Hajj alone, and we entered ihram with him. When he arrived, he said, 'Whoever does not have a sacrificial animal with him should make it an Umra.' The Prophet ﷺ had a sacrificial animal with him, so he did not exit the state of ihram."
حدثنا يزيد أخبرنا حميد
ذكرت لابن عمر أن أنسا حدثنا أن النبي ﷺ أهل بعمرة وحج فقال وهل أنس إنما أهل رسول الله ﷺ بالحج وأهللنا معه فلما قدم قال من لم يكن معه هدي فليجعلها عمرة وكان مع النبي ﷺ هدي فلم يحل
Its isnad is sahih. Humayd is Ibn Abu Humayd, al-Tawil. Bakr is Ibn Abdullah Muzani. Muslim narrated the hadith (1:353) with similar wording but at greater length, via Hushaym, from Humayd, from Bakr, who said, "I heard Anas say, 'The Prophet ﷺ pronounced the talbiyah for Hajj and Umrah together.'"Bakr said, "So I told Ibn Umar about that, and he said, 'He pronounced the talbiyah for Hajj alone.' Then I met Anas and told him what Ibn Umar had said, and Anas said, 'Do you take us for nothing but children? I heard the Messenger of Allah ﷺ say, "Here I am, for Umrah and Hajj."'"Then he narrated it again with similar wording via Yazid bin Zuray, from Habib bin Shaheed, from Bakr.It appears that Ibn Umar is the one who was mistaken, and that is why the reports from him differ as to whether the Messenger of Allah ﷺ performed Hajj alone, combined Hajj and Umrah together, or performed Umrah followed by Hajj. See Fath al-Bari 3:341, and see 4595, 4872, 4964.