Hadith 8:3234
Abu Bakr narrated to us, he said: Jarir ibn Abd al-Hamid narrated to us, from Layth, from Ata and Mujahid: They both said: The one in the state of ihram shall not put his shoulders into the qaba (a type of outer garment/coat), but there is no harm in him wrapping himself with it.
حدثنا أبو بكر قال نا جرير بن عبد الحميد عن ليث عن عطاء ومجاهد قالا لا يدخل المحرم منكبيه في القبا ولا بأس أن يرتدي به