Musnad Ahmad 27:749

Yahya narrated to us, from Ibn ‘Ajlan, from Nafi‘, who said: Ibn ‘Umar was struck by the cold while he was in the state of Ihram, so I threw a burnous (hooded cloak) over Ibn ‘Umar. He said: "Remove it from me. Do you not know that the Messenger of Allah (ﷺ) forbade the burnous for the one in Ihram?"