Musannaf Ibn Abi Shayba 1:922

Abu Khalid al-Ahmar narrated to us, from Abu Malik al-Ashja‘i [Sa‘d] ibn Tariq, who said: I said to al-Sha‘bi, "I woke up and there was a spot of seminal fluid on my garment." He said, "Rub it." Then he said, "Shake it off." I said, "Should I wash it?" He said, "That would only make it more firmly fixed." Abu Malik said: I thought that if it had been wet, he would have ordered him to wash it.