مُوَطَّأُ مَالِكٍ
Muwatta Malik 97
Purity
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، كَانَ يَقُولُ مِنْ قُبْلَةِ الرَّجُلِ امْرَأَتَهُ الْوُضُوءُ .
Yahya related to me from Malik that he had heard that Abdullah ibn Masud used to say, "Wudu is necessary if a man kisses his wife."
Arabic/English book reference: Book 2, Hadith 67