What is the evidence from the Sunnah regarding the impurity of madhi (pre-seminal fluid) if it gets on clothes, the impurity of urine even if it dries, and that prayer performed while having them on is invalid?

"Madhy (pre-seminal fluid) is impure and nullifies ablution (wudu'). The evidence for this is the Prophet Muhammad's — peace and blessings be upon him — command to wash the male organ and perform ablution from it, and to sprinkle water on whatever part of the garment it touches. Scholars have unanimously agreed on its impurity."