Musnad Ahmad 26:298

Abu al-Nadr narrated to us, Sharik narrated to us, from Ayyash al-Amiri, from al-Aswad ibn Hilal, from Ibn Mas’ud, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, among the signs of the Hour is that a man greets another man, and he does not greet him except for acquaintance."