Anas bn Malik (radhiyal Laahu 'anh) narrated:

'When some Yemeni people arrived al Madeenah, the prophet  (sallal Laahu 'alayhi wassallam) said:

"The Yemenis are around; they have tender hearts than you do." They were the first to introduce handshaking (as a form of greeting).'

 - Abu Dawud #5213,  Adabul Mufrad #967