Musannaf Ibn Abi Shayba 1:977

Waki’ narrated to us, from ‘Ikrimah ibn ‘Ammar, from ‘Abd Rabbih ibn Musa, from his mother, from ‘Aishah, who said: "For semen, ghusl (full ablution) is required. For madhy (pre-seminal fluid) and wady (prostatic fluid), one performs wudu (ablution) because of them."