Sahih Muslim 1240a

Muhammad ibn Hatim narrated this to me: Bahz narrated to us: Wuhayb narrated to us: Abdullah ibn Tawus narrated to us, from his father, from Ibn Abbas (may Allah be pleased with them), who said: They used to regard Umra during the months of Hajj as one of the most wicked practices on earth. They would treat Muharram as Safar and say: When the camel saddle sores had healed, the tracks had faded, and Safar had passed, Umra was lawful for whoever wished to perform it. The Prophet and his Companions arrived on the morning of the fourth day, having entered ihram for Hajj. He instructed them to make it an Umra. This seemed overwhelming to them, so they said: Messenger of Allah, what kind of release? He said: Complete release.