Musnad Ahmad 944:12

Waki’ narrated to us, Hisham bin ‘Urwah narrated to us, from Abu Khuzaymah, from ‘Amarah bin Khuzaymah, from Khuzaymah bin Thabit, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said regarding cleaning oneself after relieving oneself (al-istinja’): "Three stones, there is no dung (raji’) in them."