It was related to me from Malik from Musa ibn Uqba from Abd ar- Rahman ibn Yazid al-Ansari that when Anas ibn Malik came back from Iraq, Abu Talha and Ubayy ibn Kab visited him. He brought them some cooked food and they ate, and then Anas got up and did wudu. Abu Talha and Ubayy ibn Kab asked, "What's this, Anas? Is it an Iraqi custom?" and Anas said, "I wish I had not done it." (i.e. wudu). Abu Talha and Ubayy ibn Kab both got up and prayed without doing wudu.

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ زَيْدٍ الأَنْصَارِيِّ، أَنَّ أَنَسَ بْنَ مَالِكٍ، قَدِمَ مِنَ الْعِرَاقِ فَدَخَلَ عَلَيْهِ أَبُو طَلْحَةَ وَأُبَىُّ بْنُ كَعْبٍ فَقَرَّبَ لَهُمَا طَعَامًا قَدْ مَسَّتْهُ النَّارُ فَأَكَلُوا مِنْهُ فَقَامَ أَنَسٌ فَتَوَضَّأَ فَقَالَ أَبُو طَلْحَةَ وَأُبَىُّ بْنُ كَعْبٍ مَا هَذَا يَا أَنَسُ أَعِرَاقِيَّةٌ فَقَالَ أَنَسٌ لَيْتَنِي لَمْ أَفْعَلْ ‏.‏ وَقَامَ أَبُو طَلْحَةَ وَأُبَىُّ بْنُ كَعْبٍ فَصَلَّيَا وَلَمْ يَتَوَضَّآ ‏.‏
USC-MSA web (English) reference : Book 2, Hadith 27
Arabic reference : Book 2, Hadith 57