(1) The Book of Purification and its Sunnah
كتاب الطهارة وسننها
(64) Chapter: Concession concerning that
(64) باب الرُّخْصَةِ فِي ذَلِكَ
Sunan Ibn Majah 483 
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).'"
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا مُحَمَّدُ بْنُ جَابِرٍ، قَالَ سَمِعْتُ قَيْسَ بْنَ طَلْقٍ الْحَنَفِيَّ، عَنْ أَبِيهِ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ سُئِلَ عَنْ مَسِّ الذَّكَرِ فَقَالَ ‏ "‏ لَيْسَ فِيهِ وُضُوءٌ إِنَّمَا هُوَ مِنْكَ ‏"‏ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan Ibn Majah 483
In-book reference : Book 1, Hadith 217
English translation : Vol. 1, Book 1, Hadith 483