Musannaf Ibn Abi Shayba 8:308

Abu Bakr narrated to us, he said: Abu al-Ahwas (Burdah) narrated to us, from Abu al-Harith al-Tamimi, who said: I performed Tamattu' (the Umrah during the months of Hajj), then I met Ibn Abbas and said: "I have performed Tamattu', and I intend to enter into the state of Ihram for Hajj. So from where should I enter into the state of Ihram for Hajj?" He said: "From wherever you wish." He said: I said: "From the Masjid?" He said: "From the Masjid."