Musannaf Ibn Abi Shayba 3:4155

Abu Bakr narrated to us, he said: Abu Bakr ibn Ayyash and Muhammad ibn Fudayl narrated to us, from Layth, from Mujahid, who said: The Imam of the people is a guarantor, so he should not single himself out with any part of the supplication to the exclusion of them.