It is narrated from Sayyiduna Ali (may Allah be pleased with him): I felt shy, because of Sayyidah Fatimah (may Allah be pleased with her), to ask the Messenger of Allah (peace and blessings be upon him) about pre-seminal fluid (madhy). So I told a man, and he asked him (peace and blessings be upon him). He (peace and blessings be upon him) said: "For it there is ablution."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 561