Musnad Ahmad 25:654

Yazid narrated to us, Shu'bah informed us, from Qatadah, from Abu Hassan, who said: A man from Banu al-Hujaym said: "O Abu Abbas, what is this fatwa that has spread among the people: that whoever circumambulates the House (the Kaaba) has become permitted (i.e., exited the state of Ihram)?" He said: "It is the Sunnah of your Prophet, may Allah bless him and grant him peace, even if you dislike it."