وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، أَنَّهُ قَالَ كُنْتُ مَعَ عَبْدِ اللَّهِ بْنِ عُمَرَ فِي سَفَرٍ فَرَأَيْتُهُ بَعْدَ أَنْ طَلَعَتِ الشَّمْسُ تَوَضَّأَ ثُمَّ صَلَّى قَالَ فَقُلْتُ لَهُ إِنَّ هَذِهِ لَصَلاَةٌ مَا كُنْتَ تُصَلِّيهَا ‏.‏ قَالَ إِنِّي بَعْدَ أَنْ تَوَضَّأْتُ لِصَلاَةِ الصُّبْحِ مَسِسْتُ فَرْجِي ثُمَّ نَسِيتُ أَنْ أَتَوَضَّأَ فَتَوَضَّأْتُ وَعُدْتُ لِصَلاَتِي ‏.‏

Yahya related to me from Malik from Nafi that Salim ibn 'Abdullahsaid, "I was with Abdullah ibn Umar on a journey and after the sun hadrisen I saw him do wudu and then pray. So I said to him, 'This isn't aprayer that you normally do. 'He said, 'After I had done wudu for thesubh prayer, I touched my genitals. Then I forgot to do wudu. So I didwudu again and repeated my prayer.' " Translation Not Available

Book Ref: Muwatta Imam Malik Book 2 Hadith 95
Web Ref:  Muwatta Imam Malik Book 2 Hadith 65