Musnad Ahmad 30:2926

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, and Hajjaj said: Shu'bah narrated to me, from 'Asim ibn 'Ubayd Allah, from 'Ubayd, the freed slave of Abu Ruhm, from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace, that he said: "Shall I not guide you—Hajjaj said: Shall I not guide you—to a treasure from the treasures of Paradise? 'There is no power except by Allah' (La hawla wa la quwwata illa billah)."