Musnad Ahmad 28:520

'Attab ibn Ziyad narrated to us, Abdullah informed us, Usamah ibn Zayd informed us, 'Amr ibn Shu'ayb narrated to me, from his father, from Abdullah ibn 'Amr, that the Messenger of Allah (peace and blessings of Allah be upon him) would not shake hands with women during the pledge of allegiance.