Sahih Muslim Book - 3, Hadith - 828

و حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ عَنْ عَمْرٍو عَنْ سَعِيدِ بْنِ الْحُوَيْرِثِ سَمِعْتُ ابْنَ عَبَّاسٍ يَقُولُ كُنَّا عِنْدَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَجَاءَ مِنْ الْغَائِطِ وَأُتِيَ بِطَعَامٍ فَقِيلَ لَهُ أَلَا تَوَضَّأُ؟ فَقَالَ: لِمَ؟ أَأُصَلِّي فَأَتَوَضَّأَ؟.

It was narrated from Sa'eed bin Al-Huwairith: "I heard Ibn 'Abbas say: 'We were with the Prophet (s.a.w) when he came from where he relieved himself and some food was brought. It was said to him: Aren't you going to perform Wudu '? He said: Why? Am I going to prayer, that I should perform Wudu'?'"