Musnad Ahmad 32:1390

Yahya ibn Ishaq narrated to us, he said: Yahya ibn Ayyub narrated to us, Humayd al-Tawil narrated to us, he said: I heard Anas ibn Malik saying: The Prophet, may Allah bless him and grant him peace, said: "There will come to you a people who are softer in heart toward Islam than you." He said: Then the Ash'ariyyun arrived, among them Abu Musa al-Ash'ari. When they drew near to Medina, they began to chant in *rajaz* meter, and they began to say: Tomorrow we shall meet the beloved, Muhammad and his party. He said: And they were the first to introduce the handshake (*musafahah*).