كتاب الطهارة
2  
Purity

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."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، كَانَ يَقُولُ مِنْ قُبْلَةِ الرَّجُلِ امْرَأَتَهُ الْوُضُوءُ ‏.‏
USC-MSA web (English) reference : Book 2, Hadith 67
Arabic reference : Book 2, Hadith 97