Musannaf Ibn Abi Shaybah 927 — Those who said it suffices you to rub

Abu Malik al-Ashja'i said: I asked al-Sha'bi: "If in the morning I see a trace of semen, what should I do?" He said: "Rub it and shake it off." I said: "Should I wash it?" He said: "Washing will only increase its foul smell." Abu Malik said: I think that if it had been wet, he would have ordered it to be washed.