Musnad Ahmad 25:969

Abu Kamil narrated to us, Sharik narrated to us, from Muhammad ibn Abd al-Rahman, the freed slave of the family of Talhah, from Kurayb, from Ibn Abbas, who said: A woman came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, my sister has vowed to perform Hajj walking." He said: "Indeed, Allah has no need for the hardship of your sister. Let her go out riding, and let her offer an expiation for her oath."