Sayyiduna Ali (may Allah be pleased with him) says: I used to have a great deal of madhi (pre-seminal fluid), and I would take a ritual bath until my back became sore. The narrator says: I mentioned this to the Prophet (peace and blessings be upon him), or it was mentioned to him, and he (peace and blessings be upon him) said: "Do not do that. When you see madhi, wash your private part and perform ablution as you do for prayer; and when the water gushes forth (that is, semen is discharged), take a ritual bath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 799