Musnad Ahmad 30:2110

Ahmad ibn Abd al-Malik narrated to us, he said: Zuhayr narrated to us, he said: Abu Balj Yahya ibn Abi Sulaym narrated to us, from Amr ibn Maymun, that he narrated to him, he said: Abu Hurayrah said to me: The Messenger of Allah, may Allah bless him and grant him peace, said to me: "Shall I not teach you a word from the treasure of Paradise?" He said: I said: "Yes, may my father and mother be ransomed for you." He said: "Say: There is no power except by Allah (la hawla wa la quwwata illa billah)."