Musannaf Ibn Abi Shayba 8:396

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from al-A'mash, from Qays ibn Muslim, from Tariq ibn Shihab, who said: 'Abd al-Rahman was asked about the 'Umrah during the months of Hajj. He said: "The Hajj is [in] known months; there is no 'Umrah in them."