Ruling on initiating the salam when speaking on the telephone

What is the ruling on saying salam to a person to whom you are speaking on the phone, when you do not know whether he is a Muslim or not?.

Praise be to Allah, and blessings and peace be upon the Messenger of Allah:

The ruling is the same as when meeting him in person. If you know that he is a kaafir, then do not initiate the greeting. But if you do not know, there is nothing wrong with that.

And Allah is the Source of strength.