Musnad Ahmad 25:983

Rawh narrated to us, Hammad narrated to us, from Asim al-Ghanawi, from Abu al-Tufayl—Rawh said thus: Asim, and the people say: Abu Asim—he said: I said to Ibn Abbas: Your people claim that the Messenger of Allah, may Allah bless him and grant him peace, performed the circumambulation (tawaf) between al-Safa and al-Marwah on a camel, and that this is a Sunnah? He said: They spoke the truth and they lied. I said: And what is the truth and the lie? He said: He did perform the circumambulation between al-Safa and al-Marwah on a camel, but that is not a Sunnah. The people would not turn away from the Messenger of Allah, may Allah bless him and grant him peace, nor would they push back, so he performed the circumambulation on a camel so that they could listen to him, and so that they could see his position, and so that their hands would not reach him.