Musnad Ahmad 108:3

Harun ibn Ma'ruf, Surayj, and Mu'awiyah ibn 'Amr narrated to us, they said: 'Abdullah ibn Wahb narrated to us, from 'Amr ibn al-Harith, from Sa'id ibn Abi Hilal, from 'Umar ibn al-Hakam al-Ansari, from Abu al-Yusr, a companion of the Messenger of Allah, may Allah bless him and grant him peace: That the Messenger of Allah, may Allah bless him and grant him peace, said: "Among you is he who performs the prayer completely, and among you is he who performs half of it, a third, a quarter, until he reached a tenth." Surayj said in his narration: "Until he reached a tenth."