Abu al-Tufayl says: I said to Ibn Abbas (may Allah be pleased with them both): "Your people claim that the Messenger of Allah (peace and blessings be upon him) went round between al-Safa and al-Marwah riding on a camel, and that this is a Sunnah." He said: "They speak the truth and they lie." I said: "What is meant by this speaking the truth and lying?" He said: "The truth is that the Messenger of Allah (peace and blessings be upon him) did perform the tawaf on a camel, and the lie is that it is a Sunnah. People were not driven away from the Messenger of Allah (peace and blessings be upon him), so he (peace and blessings be upon him) performed the tawaf on a camel so that the people could see him and hear his words, and their hands could not reach him (peace and blessings be upon him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9379