(a) Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says concerning semen (mani), pre-seminal fluid (madhy) and post-urinary discharge (wady): For semen there is a ritual bath (ghusl), and for pre-seminal fluid and post-urinary discharge there is ablution; (such a person) should wash his private part and perform ablution.
(b) Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: Wady comes after urinating, and for it there is ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 564