Musnad Ahmad 5:727

Abdullah narrated to us, Ibrahim ibn al-Hajjaj al-Naji narrated to me, Hammad ibn Salamah narrated to us, from Hisham ibn Amr al-Fazari, from Abd al-Rahman ibn al-Harith ibn Hisham, from Ali ibn Abi Talib: That the Messenger of Allah, peace and blessings of Allah be upon him, used to say at the end of his Witr: "O Allah, I seek refuge in Your pleasure from Your wrath, and in Your pardon from Your punishment, and I seek refuge in You from You. I cannot enumerate Your praise; You are as You have praised Yourself."