Musnad Ahmad 1153:1464

'Abd al-Rahman narrated to us, from Sufyan, from al-A'mash, from Abu al-Duha, from Masruq, from 'A'ishah, who said: The Messenger of Allah (may Allah bless him and grant him peace) granted a concession regarding a certain matter, but some men refrained from it. He said: "What is the matter with men whom I command to do a thing, yet they refrain from it? By Allah, I am the most knowledgeable of them regarding Allah, the Mighty and Majestic, and the most intense of them in fear of Him."