Musnad Ahmad 32:1101

Marwan ibn Mu'awiyah narrated to us, Hanzalah ibn Abdullah al-Sadusi narrated to us, he said: Anas ibn Malik narrated to us, he said: A man said: "O Messenger of Allah, one of us meets his friend, should he bow to him?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "No." He said: "Should he embrace him and kiss him?" He said: "No." He said: "Should he shake his hand?" He said: "Yes, if he wishes."