From Sahih Muslim (Hadith 3013):
Ibn Abbas (Allah be pleased with them) reported that Allah's Messenger (ﷺ) observed the morning prayer at Dhu Tawa (a valley near Mecca) and arrived (in Mecca) when four days of Dhul-Hijja had passed and he commanded his Companions that they should change their Ihram (of Hajj) to that of Umra, except those who had brought sacrificial animals with them
Reference: Muslim 3013