I say, and with God's success: Al-Wadi is a thick white fluid that has no smell, which comes out after urination. It necessitates ablution, not a full wash; because it is a result of urination, it requires ablution due to it being impure. It was narrated that Mujahid said a man asked Ibn Abbas (may Allah be pleased with him): "Whenever I urinate, a flowing fluid follows that is from which a child is produced... He said: Do you feel desire in your heart? He said: No. He said: Do you feel numbness in your body? He said: No. He said: This is merely a discharge, and you are excused from it with ablution." This was narrated by Al-Hakim in his history, and its chain of narration is good. See: I'laa as-Sunan 1: 189. Also see: Rad al-Muhtar 1: 107, Umdat al-Ri'ayah 1: 81, Al-Lubab 1: 16, and Talabat al-Talabah p. 18, and Allah knows best.