Jundub, the freed slave of Abdullah bin Ayyash bin Abi Rabi'ah al-Makhzumi, says: I asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) about madhi (pre-seminal fluid), and he said: "When you find it, wash your private part and perform ablution as for prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1668