حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ أَبِي النَّضْرِ، مَوْلَى عُمَرَ بْنِ عُبَيْدِ اللَّهِ عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، عَنِ الْمِقْدَادِ بْنِ الأَسْوَدِ، أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ، أَمَرَهُ أَنْ يَسْأَلَ، لَهُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنِ الرَّجُلِ إِذَا دَنَا مِنْ أَهْلِهِ فَخَرَجَ مِنْهُ الْمَذْىُ مَاذَا عَلَيْهِ قَالَ عَلِيٌّ فَإِنَّ عِنْدِي ابْنَةَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَنَا أَسْتَحِي أَنْ أَسْأَلَهُ ‏.‏ قَالَ الْمِقْدَادُ فَسَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ ذَلِكَ فَقَالَ ‏"‏ إِذَا وَجَدَ ذَلِكَ أَحَدُكُمْ فَلْيَنْضَحْ فَرْجَهُ بِالْمَاءِ وَلْيَتَوَضَّأْ وُضُوءَهُ لِلصَّلاَةِ ‏"‏ ‏.‏

Yahya related to me from Malik from Abu'n Nadr, the mawla ofAbdullah ibn Ubaydullah, from Sulayman ibn Yasar from alMiqdad ibn al-Aswad that Ali ibn Abi Talib told him to ask the Messenger of Allah,may Allah bless him and grant him peace, what a man should do, who,when close to his wife, had a flow of prostatic fluid. Ali explainedthat the daughter of the Messenger of Allah, may Allah bless him andgrant him peace, was living with him then and he was too shy to askfor himself. Al-Miqdad said, "I asked the Messenger of Allah, mayAllah bless him and grant him peace, about it, and he said, 'When youfind that, wash your genitals with water and do wudu as for prayer.' " Translation Not Available

Book Ref: Muwatta Imam Malik Book 2 Hadith 85
Web Ref:  Muwatta Imam Malik Book 2 Hadith 55