Musnad Ahmad 33:1012

Surayj ibn al-Nu‘man narrated to us, Sa‘id—meaning Ibn Zayd—narrated to us, from ‘Amr ibn Dinar, Jabir ibn ‘Abd Allah narrated to me, he said: A man from the Emigrants (Muhajirun) struck a man from the Helpers (Ansar) on the buttocks. The Ansari said: "O for the Ansar!" And the Muhajiri said: "O for the Muhajirun!" The Messenger of Allah, peace and blessings of Allah be upon him, said: "What is this call of the pre-Islamic era (Jahiliyyah)? The call of the striking of the buttocks? For it is foul-smelling."