Musnad Abu Ya'la al-Mawsili 111:42

Abdullah ibn Umar ibn Aban narrated to us, Talha ibn Sinan narrated to us, from Abu Sa’d, from Ikrimah, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent for a man from the Ansar, but he was slow in coming to him. He said, "What kept you?" He said, "I was with my wife when your messenger came to me, so I stood up and performed ghusl (ritual bath)." He said, "What was upon you that you did not perform ghusl as long as you did not ejaculate?" He said, "The Ansar used to do that."