Qais bin Talq Al-Hanafi narrated that his father said:
"I heard the Messenger of Allah being asked about touching the penis. He said: 'That does not require ablution, because it is a part of you (your body).'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 483 (IT)
Arabic reference (IT): Book 1, Hadith 521 (IT)