Musnad Ahmad 30:361

Yazid narrated to us, Isma'il informed us, from Ziyad al-Makhzumi, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "None of you will enter Paradise by his deeds." They said: "Not even you, O Messenger of Allah?" He said: "Not even me, unless Allah covers me with mercy and grace from Him." And he placed his hand upon his head.