Musnad Ahmad 937:10

Ammar ibn Muhammad narrated to us, from al-A’mash, from Mujahid, from Abd al-Rahman ibn Abi Layla, from Abu Dharr, who said: The Messenger of Allah (may Allah bless him and grant him peace) said to me: "O Abu Dharr, shall I not guide you to a treasure from the treasures of Paradise? Say: There is no power and no strength except by Allah."