It is narrated from Sayyiduna Miqdad bin al-Aswad (may Allah be pleased with him) that Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) told him to ask the Messenger of Allah (peace and blessings be upon him) about one of us: when pre-seminal fluid comes out of him, what is required of him? "For his daughter is married to me, and I feel shy to ask." Miqdad (may Allah be pleased with him) said: I asked him (peace and blessings be upon him), and he (peace and blessings be upon him) said: "When one of you finds that (pre-seminal fluid), let him wash his private part and perform ablution as he does for prayer."
(b) This narration is also transmitted from Sayyiduna Ibn Abbas (may Allah be pleased with them both) in connected (mawsul) form.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 562