حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ أَبِي النَّضْرِ، عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، عَنِ الْمِقْدَادِ بْنِ الأَسْوَدِ، أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ، - رضى الله عنه - أَمَرَهُ أَنْ يَسْأَلَ لَهُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنِ الرَّجُلِ إِذَا دَنَا مِنْ أَهْلِهِ فَخَرَجَ مِنْهُ الْمَذْىُ مَاذَا عَلَيْهِ فَإِنَّ عِنْدِي ابْنَتَهُ وَأَنَا أَسْتَحْيِي أَنْ أَسْأَلَهُ ‏.‏ قَالَ الْمِقْدَادُ فَسَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَنْ ذَلِكَ فَقَالَ ‏"‏ إِذَا وَجَدَ أَحَدُكُمْ ذَلِكَ فَلْيَنْضَحْ فَرْجَهُ وَلْيَتَوَضَّأْ وُضُوءَهُ لِلصَّلاَةِ ‏"‏ ‏.‏

Narrated Al-Miqdad ibn al-Aswad: Ali ibn AbuTalib commanded him to ask the Messenger of Allah (PBUH) what a man should do when he wants to have intercourse with his wife and the prostatic fluid comes out (at this moment). (He said): I am ashamed of consulting him because of the position of his daughter. Al-Miqdad said: I asked the Messenger of Allah (PBUH) about it. He said: When any of you finds, he should wash his private part, and perform ablution as he does for prayer. Translation Not Available

Book Ref: Sunan Abi Dawud Book 1 Hadith 207
Web Ref:  Sunan Abi Dawud Book 1 Hadith 207