Sayyiduna al-Hakam bin Umayr (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) said: "When one of you performs the ritual bath (ghusl) and then something (some fluid) appears from his private organ, let him perform ablution."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3172