Musnad Abu Ya'la al-Mawsili 115:30

Hadbata narrated to us, Hammam narrated to us, Qatadah narrated to us, he said: I said to Anas, "Was the handshake (practiced) during the time of the Messenger of Allah, may Allah bless him and grant him peace?" He said, "Yes." Qatadah said, "And Al-Hasan used to shake hands."