Musannaf Ibn Abi Shayba 3:4156

Ibn ‘Ulayyah narrated to us, from Khalid al-Hadhdha’, who said: Abu Qilabah said: "Do you know why I disliked leading the prayer (imamah)?" He said: "No." He said: "But it was disliked because it is not for an Imam to single himself out with a supplication to the exclusion of those behind him."