Musnad Ahmad 28:597

'Abd al-Jabbar ibn Muhammad—meaning al-Khattabi—narrated to us, Baqiyyah narrated to me, from Muhammad ibn al-Walid al-Zubaydi, from 'Amr ibn Shu'ayb, from his father, from his grandfather, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to me: "Whoever touches his penis, let him perform ablution, and whichever woman touches her private part, let her perform ablution."