Musnad Ahmad 363:1

Abu Bakr al-Hanafi narrated to us, he said: Ibn Ja’far narrated to us, from ‘Amr ibn Shu’ayb, from the daughter of Kardama, from her father, that he asked the Messenger of Allah, peace and blessings of Allah be upon him, and said: "I have vowed to slaughter three of my camels." He said: "If it is for a gathering of the gatherings of Jahiliyyah (pre-Islamic ignorance), or for an Eid of the Eids of Jahiliyyah, or for an idol, then do not. But if it is for other than that, then fulfill your vow." He said: "O Messenger of Allah, the mother of this girl has a vow of walking (on foot to a place of worship), shall I walk on her behalf?" He said: "Yes."