Musnad Ahmad 27:1425

Hussain ibn Muhammad narrated to us, Ayyub ibn Jabir narrated to us, from Abdullah—meaning Ibn 'Ismah—from Ibn Umar, who said: "The prayer was fifty, and the washing from major ritual impurity (janabah) was seven times, and the washing from urine was seven times. The Messenger of Allah (ﷺ) did not cease asking until the prayer was made five, and the washing from major ritual impurity was once, and the washing from urine was once."