Sahih Bukhari Volume 001, Book 004, Hadith Number 179.

Narated By Zaid bin Khalid : I asked 'Uthman bin 'Affan about a person who engaged in intercourse but did no discharge. 'Uthman replied, "He should perform ablution like the one for ar ordinary prayer but he must wash his penis." 'Uthman added, "I heard it from Allah's Apostle." I asked 'Ali Az-Zubair, Talha and Ubai bin Ka'b about it and they, too, gave the same reply. (This order was cancelled later on and taking a bath became necessary for such cases).