Musnad Ahmad 30:313

Abdullah narrated to us, Yahya ibn Ma'in narrated to us, Hafs narrated to us, from al-A'mash, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever overlooks the stumble of a Muslim, Allah will overlook his stumble on the Day of Resurrection."