The Cleansing of Impurities - Section 1 Mishkat al-Masabih 495, 496
Translation
Al-Aswad and Hammam reported ‘A'isha as saying, “I used to rub the prostatic fluid from the garment of God's messenger." Muslim transmitted it. A version of ‘Alqama and al-Aswad quotes ‘A'isha to the same effect, with the addition that he then prayed in it.