Muwatta Imam Malik Book of Purity, Hadith 65

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

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 .