What is the ruling on not greeting with "peace" except those whom you know?

We are advised to spread greetings of peace (Salām) to those we know and those we do not know. This is one of the best qualities of Islam, as indicated by the Prophet, peace and blessings be upon him, in the hadith: "Which aspect of Islam is best?" He replied: "You feed the hungry and you offer greetings of peace to those you know and those you do not know." This means offering greetings to everyone you meet, whether you know them or not.