Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him) said: Among the signs of the Hour is that a man will greet another man with Salam only because of acquaintance.
Hadith Referenceالفتح الربانی / كتاب السلام والاستئذان وآداب أخرى / 8258
Benefits: … The Noble Prophet sallallahu alayhi wa sallam has commanded the spreading of salam (greeting of peace). Furthermore, a Muslim is greeted with salam because Allah Ta'ala and His Messenger have commanded it. If a person offers salam based on personal acquaintance, then in reality, it is not in accordance with the command of Allah Ta'ala and His Messenger. However, this is exactly what is happening now, which the Prophet sallallahu alayhi wa sallam had described as a sign of the Last Day. Now, in order to greet someone with salam, it has become necessary to have personal acquaintance; the situation of strangers is no better than that of the mute.