From ancient times, the prophets of God including Moses, Joseph, David, Jesus, the angles of God and many others have made it their custom to greet the believers with the words "Peace be with you." This can be seen in such verses as:
 

Genesis 43:23"And he said, Peace be to you, fear not: your God, and the God of your father, hath given you treasure in your sacks: I had your money. And he brought Simeon out unto them."

Judges 6:23"And the LORD said unto him, Peace be unto thee; fear not: thou shalt not die."

1 Samuel 25:6"And thus shall ye say to him that liveth in prosperity, Peace be both to thee, and peace be to thine house, and peace be unto all that thou hast."

Numbers 6:26"The LORD lift up his countenance upon thee, and give thee peace."

1 Samuel 1:17"Then Eli answered and said, Go in peace"

Luke 24:36"And as they thus spake, Jesus himself stood in the midst of them, and saith unto them, Peace be unto you."

John 20:19".....came Jesus and stood in the midst, and saith unto them, Peace be unto you."

John 20:26"........then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you."

And especially:

Luke 10:5"And into whatsoever house ye enter, first say, Peace be to this house."
 

Can anyone guess what Muhammad (pbuh) taught his followers to say when greeting each other or departing from each other? You guessed it! "Assalam alaikum" or "Peace be unto you." Have you ever met a Christian who greets others with the words of Jesus (pbuh): "Peace be unto you" or departs with those words?