Musnad Abu Ya'la al-Mawsili 107:20

Abu Khaythama narrated to us, Yahya ibn Sa'id al-Qattan narrated to us, from Yahya, he said: 'Abdullah ibn Zahr narrated to me, that Abu Sa'id informed him, that 'Abdullah ibn Malik informed him, that 'Uqbah ibn 'Amir informed him: That he asked the Messenger of Allah (may Allah bless him and grant him peace) about his sister who had made a vow to walk barefoot and unveiled. So he commanded her to cover her head, ride, and fast for three days.