Ash-Shama'il Al-Muhammadiyah, Book 26, Hadith 177 (English) ⓘ

Ibn 'Abbaas Radiyallahu 'Anhu relates: "Rasulullah Sallallahu 'Alayhi Wasallam once, after relieving himself in the toilet, came out, and was served food. The Sahaabah inquired: 'Will you not perform wudu?'. Rasulullah Saliallahu 'Alayhi Wasallam replied: 'Do I have to perform salaah, that wudu must be performed?'"

حَدَّثَنَا سَعِيدُ بْنُ عَبْدِ الرَّحْمَنِ الْمَخْزُومِيُّ، قَالَ‏:‏ حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ عَمْرِو بْنِ دِينَارٍ، عَنْ سَعِيدِ بْنِ الْحُوَيْرِثِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ‏:‏ خَرَجَ رَسُولُ اللهِ صلى الله عليه وسلم مِنَ الْغَائِطِ فَأُتِيَ بِطَعَامٍ، فَقِيلَ لَهُ‏:‏ أَلا تَتَوَضَّأُ‏؟‏ فَقَالَ‏:‏ أَأُصَلِّي، فَأَتَوَضَّأُ‏.‏