Musannaf Ibn Abi Shayba 1:1779

Khalid ibn Hayyan narrated to us, from Ja’far, who said: A man came to Maymun ibn Mihran and complained to him about moisture he was finding. Maymun said to him: "When you perform wudu, sprinkle your private part and what is adjacent to it of your garment with water. Then, if you find anything of that [moisture], say: 'It is from that.'"