Musannaf Ibn Abi Shayba 1:17

Khalaf ibn Khalifah narrated to us, from Layth, from Husayn ibn 'Umarah, from Abu Bakr, who said: When the servant performs ablution and mentions the name of Allah during his ablution, his entire body becomes purified. And when he performs ablution and does not mention the name of Allah, only that which the water touched becomes purified.