Musnad Ahmad 30:2562

Muhammad ibn Ubayd narrated to us, he said: Al-A’mash narrated to us, from Abu Salih, from Abu Hurayrah, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Two things are among the people [that are acts of] disbelief: wailing over the dead, and slandering lineage."