Sahih Muslim
The Book of Vows (Kitab Al-Nadhr)
Book Number: 014 / Hadith Number: 4032
'Uqba b. Amir reported: My sister took a vow that she would walk bare foot to the house of Allah (Ka'ba). She asked me to inquire from Allah's Messenger (may peace be upon him) about it. I sought his decision and he said: She should walk on foot and ride also.