Muwatta Malik 93

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، أَنَّهُ قَالَ رَأَيْتُ أَبِي عَبْدَ اللَّهِ بْنَ عُمَرَ يَغْتَسِلُ ثُمَّ يَتَوَضَّأُ فَقُلْتُ لَهُ يَا أَبَتِ أَمَا يَجْزِيكَ الْغُسْلُ مِنَ الْوُضُوءِ قَالَ بَلَى وَلَكِنِّي أَحْيَانًا أَمَسُّ ذَكَرِي فَأَتَوَضَّأُ ‏.‏

Yahya related from Malik from Ibn Shihab that Salim ibn Abdullah said, "I saw my father Abdullah ibn Umar, do ghusl and then do wudu. I said to him, 'Father, isn't ghusl enough for you?' He said, 'Of course, but sometimes I touch my penis, so I do wudu

Reference

Muwatta Malik 93

In-book

Book 2, Hadith 62