The Prophet ﷺ entered the state of ihram immediately after completing the prayer.
حدثنا قتيبة حدثنا عبد السلام بن حرب عن خصيف عن سعيد بن جبير
أن النبي ﷺ أهل في دبر الصلاة
No references are available.
[Its chain of transmission is daif] Nasai also narrated it in Manasik Hajj, chapter on the action during ihlal, 5/162, hadith 2755, from Qutayba through the same chain. Khaseef is daif.